List of ''Eureka'' episodes

While transporting his delinquent daughter back to Los Angeles, U.S. Marshal Jack Carter crashes his car near Eureka. There, he assists in a case involving a tachyon accelerator. The town begins to experience time and space anomalies. When Carter investigates these incidents, Jim Taggart kidnaps him and Carter meets Allison Blake, who shows him Global Dynamics (GD) and the real side of Eureka.

Carter must help an aged scientist recover his memory in time to stop a doomsday device from destroying the world. The old scientist, Dr. Thatcher, has not been the same ever since he didn't win the Nobel Peace Prize for creating a mutual assured destruction (M.A.D) device, which fires a beam of irradiated uranium isotopes at a mirror on the moon, bouncing back at Earth to hit another target on its surface after Earth has rotated sufficiently (mostly likely causing World War III, since the default target was chosen during World War II).

Nathan Stark is given the opportunity to investigate "the Artifact." After it is tested (with Kim's help), we cut to 2010 and Eureka is a very different place. Stark is a billionaire in California, Henry is married to Kim as well as the principal of Tesla High school and the head of Global Dynamics. Carter and Allison are married, and Allison is pregnant. Zoe is the valedictorian of her class, which is graduating that day. Jo and Taggart are dating. But soon problems start to appear all over town: things that the town has experienced in the past 4 years start to happen again, a tornado nearly destroying half of downtown Eureka. Also, a body is found in Section 5, near the Artifact. They test it and find that the body belongs to Kim Deacon, Henry's wife. Henry explains that back in 2006, during Stark's test on the Artifact, Kim was extracting a sample when an explosion occurred, killing her. Henry then used Walter Perkins's tachyon accelerator to go back in time and stop her from dying. This new timeline caused all of the anomalies. The past must be fixed. Stark comes to town to help with the tachyon accelerator. Carter goes back to 2006 and stops Henry from saving Kim in the explosion. The timeline is fixed. We also learn that Beverly had implanted a chip in Nathan's neck so that the Consortium can gain second-hand access to the Artifact.

A solar eclipse happens in Eureka. Following the restoration of the timeline, Carter and Henry must adjust, while Allison gets Nathan's job, and citizens of Eureka start to spontaneously combust. Three of these victims are scientists, all of them having little to no relation to one another. One of them is Kevin's (Allison's son) therapist. Kevin hints that when he went to therapy, he would sometimes go to "the man downstairs". Carter tries to get Henry to help him adapt more to the timeline. Carter follows many leads to the possible deaths, he even suspects Henry at one point, also blaming Vincent's five-alarm chili. Through investigating he finds out that all three scientists were in a lab adjacent to the Artifact during the explosion, and radiation from the explosion infects them, and later causes the body's electrical system to overload. They also discover that Kevin was in the lab as well, but he is unaffected. They conclude that Stark was infected, too, so Stark (who no longer works at GD) sneaks in and goes to the Artifact chamber, just to find that it is dead: instead of a fireball, the Artifact now looks like a mass of roots. They get Stark into a lab and attempt to cool him down, they discover that they can stop him from combustion by electrically shocking his brain. They do this and it nearly kills him but he is brought back, safe from combustion. The episode ends with Henry erasing Carter's memory of the alternate timeline, and Henry then destroying the memory erasing device, saying he is never going to forget.

Nathan Stark and Jack Carter must put aside their rivalry to stop a deadly bacteria from destroying the town and killing Allison's son Kevin. Allison, Kevin, Henry, and Beverly are a mile beneath GD in a bunker, and Henry forces Allison to open up a room that contains a teleportation device, and they will use this escape method to separate Kevin from the Artifact. Meanwhile Carter, Taggert, and Stark get in protective gear and go into quarantined Section 4, which is filled with rubble when the beams were degrading in All That Glitters.... They find many people in the morgue, where the infection supposedly began, but they are just fine. Taggert attempts to lead people out of Section 4 but the defense systems pretend to be Fargo. Henry and Beverly decide it is time to teleport Kevin to the other bunker, where the Consortium can get him. Before this happens, Allison attacks Beverly, a brutal fight ensues, and Beverly is knocked out. Allison then threatens to kill Henry. Kevin intervenes and tells her to stop. Henry reveals that he was on Allison and Stark's side all along. Fargo and Zane almost have control of GD. Beverly wakes up with a knife and tries to stop Henry. Carter and Stark then appear. Stark says that the teleporter is not ready to make a successful transport. Henry says that he has calibrated it to separate Kevin from the Artifact. Kevin is placed inside the teleportation device. Jo tries to convince General Mansfield not to thermo-clean GD. Beverly uses the teleporter. Taggert is successful in leading everyone out of Section 4. Stark tells Mansfield that Beverly is dead. Henry admits to the General he was responsible for all of it. Henry is taken away by the military for his crimes.

Success comes at a price, as several citizens of Eureka discover when the DOD sends corporate fixer Eva Thorne, reputed for completely revamping more Fortune 500 companies than anyone else, to town during an Anti-Missile test that sees the target drone named Martha threatening Eureka. Martha terrorizes the town, blowing up the Viper (a weapon that shot down all other drones like her) and stalks Carter, destroys Carter's car, and attacks Carter and Jo at the sheriff's office. They discover that Martha went from having the mindset of a toddler to the mindset of a teenager, and find out that the wife of the scientist who built her increased Martha's intelligence. At Cafe Diem Martha befriends Zoe and attacks Thorne and her escort, the suck-up (and Fargo's arch nemesis) Larry. Larry is knocked unconscious. Martha is taken to GD. Carter and Jo investigate and find a remote control device on her. They discover that Larry put the device on her so he could control her and impress Thorne. However, with her teenage mindset Martha did not care for being controlled and attacked him. At Global Dynamics Martha wakes up and releases other drones similar to her. The fleet of drones heads toward Eureka, and begin taking down the EM shield that would keep them inside of the Eureka city limits. Thorne calls in a squadron of F-16's to stop the drones just in case they escape. Carter, Stark, Fargo, and Allison think that Martha just wants room to breathe, and she feels that she cannot do that inside of the EM shield. But Martha may also be trying to prove herself as being independent and may plan world domination, which would cause World War III. So they purposefully take the EM shield down, hoping Martha will see it as an olive branch. The drones and the F-16's charge each other and Zoe (understanding what Martha is going through) talks to Martha over the radio and is able to convince her to come back to Eureka. The drones disengage and return to Global Dynamics.

Carter must take the bi-annual D.O.D. re-certification test in order to remain sheriff of Eureka. The test takes 48 hours and the test is conducted completely isolated from the rest of the town. Jo passes her test with a perfect score, only to be disappointed when Zane tells her that no-one is perfect. She then fills in as acting sheriff while Carter is taking the test, as well as taking care of Zoe while Carter is otherwise occupied. Allison wants to put a new security measure into effect that uses a DNA scan to grant or deny access to various points of Global Dynamics. Henry doesn’t want to install the new devices, so Jo is called in as the deciding vote. Jo decides to have the devices installed and is the first one scanned for identification, but the device malfunctions and nearly electrocutes her. When Jo comes to it is discovered that someone had stolen a critical piece of the device. Allison wants to pull Carter out of his test to have him help find the thief, but Jo insists that she can track down the thief herself. When Jo asks Henry about the missing piece of equipment, he tells her that he is also missing an important piece of equipment. Leaving Henry to ponder a possible link between the two stolen items, Jo heads for the Smart House to help Zoe with homework. Jo finds that walking a mile in Carter's shoes is proving to be a challenge, especially when Zoe wants to blow off work and go to karaoke night at Café Diem. Jo's still feeling the effects of her near-electrocution and forbids it, wanting nothing more than to sleep. Zoe uses this as an opportunity to sneak out. Jo soon catches Zoe performing at the Café. Yet instead of grounding her, Jo joins in the fun, drinking too much as she sings and flirts with Fargo. Jo ends up kissing Fargo just as Zane enters the Café. Jo insists that she's fine, but Allison and Henry worry about Jo's state of mind after she begins behaving more erratically. Zane is worried about her behavior and convinces Fargo that she would not have kissed him if she had been her normal self. A third theft then occurs and the DNA scanner identifies Jo as the thief. Only Jo knows that someone is stealing her identity, gene by gene. Trapped in that person's body, Jo has to convince a skeptical Zane of her true identity. Fargo confronts 'Jo' getting the thief to admit their true identity. A worried Zane looks on as Henry attempts to stabilize Jo's DNA. As she shifts back to her own form, Jo ask Zane how she looks, to which he replies 'Perfect'.

Several mysterious events take place after Dr. Drechmeyer is supposedly contacted by his late mother, a famed clairvoyant. He thinks that the readings on his new energy-measuring device indicate the presence of ghosts. His lab partner and ex-wife, Mary-Beth Curtis, fears his obsession will cost them their funding, but something strange is happening. Carter finds a car parked in the middle of the road, but its driver – a spirited and beautiful new arrival, Dr. Tess Fontana – denies leaving it there. Tess leaves Carter annoyed, yet intrigued. Meanwhile, Carter's sister, Lexi, enjoys her new "Invis-Apparel" maternity shirt courtesy of GD, which completely hides her pregnant tummy. It also proves useful when the twins' world-traveling father arrives in town unannounced. Lexi hides her condition, not sure that Duncan is fatherhood material, much to Zoe's disapproval. Later, at Café Diem, Carter finds a highly agitated Dr. Drechmeyer claiming the high readings he sees prove the spirits are active. Suddenly, various objects begin to fly about and Carter has to tackle Tess Fontana to keep the espresso machine from decking her. Then, to Carter's surprise, Allison arrives and greets Tess with open arms. They are old college friends and she's been brought in for a secret project. Following another energy burst, Allison admits that GD has decided to re-open Section 5 under Tess's oversight. And she wants Carter and Tess to work together to solve the paranormal activity — even though they clearly can't stand each other. When Tess gives Carter a tour, they encounter a strange device, and some odd sensations, in one of the labs. Leaving the area, they realize that no one can see or hear them. This causes them to ponder whether they are dead; however, Tess believes they've somehow crossed into another dimension. Returning to the lab, they find Dr. Johnson recovering from an unsuccessful attempt to break out. His research on inter-dimensional travel created a temporary door into the Fifth Dimension. Unless they can re-calibrate Johnson's device before Henry and Allison unknowingly shut it down from the other side, the trio could be trapped inside forever.

Fargo, Lucas, and "The Cleaner" (and bowling champ) Big Ed Fowler, prepare their team for the bi-annual bowling competition against hated rival Toby Bismark and his team from Area 51. "Creative enhancement of odds" (cheating) is all part of the game. However, cheaters never prosper and the Eureka team members literally find themselves turning green with envy when they are dosed with gamma radiation. Meanwhile, Allison and Tess are trying to get a clear view of the distant source of a mysterious signal from space. Needing more power for the telescope, they ask Carter and Jo to confiscate all of the Globidium power cells around town. The sites that use the plutonium-like element include Café Diem and the Smart House. Making their rounds, Carter and Jo discover that someone is stealing the radioactive fuel cells. By the time Carter determines that Big Ed is the Globidium thief, there is nothing left of "The Cleaner" but a pool of green goo. It seems that Big Ed had a pet project that grew out of control. Carter and Tess find a container for Ed's radiation-devouring microorganism that is now empty. It seems the blob had Ed for lunch and has now gone out for dinner. "Team Green" would be a likely target but Duncan, returning to confront Lexi, concocts a mud bath to cure their radioactive condition. In a scene reminiscent of "Psycho", the radiation-starved blob attacks. Carter comes to the rescue, but the mutating green menace retreats down the drain and heads for Eureka's last source of Globidium — the Smart House. Zoe is safe at work but if Carter's final, desperate plan fails, Lexi and Duncan may not live to become parents.

Five unfinished plasma generators made out of scrap from all over Eureka appear in the woods outside of town. Carter and Tess stake out the site under the theory that whoever is building it will want to finish it. When night falls, all the teenagers of Eureka walk to the machines and start to augment them with new parts from town. Carter takes the teenagers (including Zoe) to the GD infirmary where when they wake up have no memory of ever building this device. The next night, the teenagers begin to try to continue building but the GD security stops them. However, other members of the town have fallen under the influence (including Zane) and they continue the construction. Carter and Henry realize that the affected are the people of the town whose cars have been integrated into the Smart Asphalt automatic driving system. The grid is shut down and all those affected fall into a coma. However the signal from space has been discovered to be the source of the sleepwalkers and it has gotten so close to the Earth that it doesn't need the Smart Asphalt system to build its device. The people of Eureka finish the machine and it creates a torrent of blue energy that shoots up into the sky. Allison prepares to shoot down the incoming ship until Fargo arrives. Fargo, who was previously held hostage by his car's AI system (Tabitha), arrives on the scene to tell Alison that the device that everyone has been building is a Boson Cloud Exciter, a catcher's mitt for a Faster than Light space jump. The ship lands, Henry approaches it and scrapes some dust of the side revealing a US flag, thus revealing that the ship is of earthly origins.

The gang begins seeing visions of people from their pasts, leading to resolutions for some, and a confrontations for others. Meanwhile, the town seems to be collapsing around them and Dr. Grant gets involved with a mysterious faction.

140 Days remaining until the Astraeus Mission Launch.

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(This is a holiday special, and takes place outside the main story.) Crashing over Eureka, a wave of color changes the town to animation of multiple styles and cartoonish effects, including Jack's jeep coming alive, Andy being turned into a cartoonish robot, and Jo becoming a princess. All this caused by the Super Photon Generator, a massive holographic matrix meant as Jack's Christmas gift for the kids (with help from Fargo). Meanwhile, Kevin, Zoey, and Jenna opened a gift early called "Holotown", a 'create your own story' book using holograms. It turns out that the gift the kids opened crossed signals with the Super Photon Generator. As the episode goes on, with the main characters aware of the changing animations, the kids add villainous Snow Ninjas to spice up the story. As Jack, Andy, Allison, and Jo make it to the generator, they see Dr. Drummer- a scientist from the last holiday special- trying to fix the generator; but as he is, the snow ninjas join to create a 50 foot snow monster. The kids realize the connection between the generator and their book and give the others a fighting chance with Kevin turning them into Anime to defeat the snow ninja monster. Jack gets Jo close enough to throw a bomb into the monster, blowing it up. As the others fight the Snow Ninja Monster, Allison, Andy, and Dr. Drummer finally repair the generator, returning everyone to normal perspective. At the end of the episode, everyone gets together for a Christmas dinner at the smart house.

The Simulation begins to unravel when Fargo decides to leave Eureka for the airport which is where he thinks Holly is going, as he is driving the stretch of road that has the Leaving Eureka sign on it repeats over and over again. Zane sees a bird get stuck in a rock and goes to investigate, Virtual-Carter goes to help and tries to dissuade Zane which proves futile when Virtual-Carter's avatar starts to glitch. In the real world, Beverly Barlowe returns to Eureka to help Carter rescue the crew, because of Senator Wen's murder of Holly Marten. She plugs Carter into the simulation to replace Virtual-Carter just before he kills Zane. They collaborate with the rest of the main Astraeus crew to destroy the virtual version of the ship. Attempting to construct an explosion of this magnitude will make the Central Processor overheat which Henry can track in the real world. This works but the explosion causes a Cascade failure in the system, the simulation begins to collapse with the Astraeus crew still inside. They give Zane an electrical shock in order to interrupt the signals exchanged between the computer and Zane's brain effectively ejecting him from inside the simulation. Zane wakes up to the barrel of one of the Consortium soldier's guns. Jo arrives just in time to stop Zane from getting shot. Zane ejects everyone but Carter from the simulation. Someone (Wen) logs Beverly out of the system so she can't eject the Sheriff, then Senator Wen and a large group of soldiers storm Henry's garage and try to disconnect Carter from the Mainframe. Henry pulls a stun grenade on everyone but Beverly, including himself, trusting Beverly with Carter's life. Beverly gets Zane to log her back on and ejects Carter, she then kidnaps senator Wen and plugs her into the simulator, trapping her in a looping virtual version of the Sheriff's office.

Zane restarts the Computer Matrix Mainframe that created the virtual Eureka in the hopes of recovering some of the corrupted data. The Mainframe begins to search for the people that were plugged into it during Senator Wen's neural experiment. Carter, as the only person who was connected wirelessly, is found and the Computer starts to stimulate his brain – causing him to swap bodies with Astraeus crew members around him. Warren Hughes, the DOD relationship auditor arrives to make sure that those involved in the neural network are ready to return to work. Carter's body swapping lands him in a load of trouble as he is forced to take not only Fargo's rehabilitation test but Zane's as well. Machines malfunction all over GD and the cause is the members of the Astraeus crew. In the end Zane discovers that the Computer Matrix has found one other member of the experiment, Holly. Zane tells Fargo that she may still be alive within the program and Fargo must make a terrible choice between leaving the machine running and trying to save Holly or shutting it down to stop it from destroying the Sheriff's mind. After the Computer Matrix almost kills him, Carter proposes to Allison, telling her that after almost dying he realizes what is truly important and he doesn't want to wait any longer to start building a life with her.

Henry starts a lifelike disaster-preparedness simulation in the aftermath of the Astraeus incident in the first three episodes. It starts with the town under attack and ends with Carter not carrying Fargo down 72 flights of stairs with a broken leg. The DOD preparedness advisor Dr. Michael Clark gives everyone an overall B+ from 29 dead and over 300 injured in the scenario. Afterwards, the hard drive containing ADA (Advanced Disaster Accuator) is destroyed by a liquid nitrogen pipe rupture. As the day continues, GD begins to experience malfunctions and breaches identical to the simulation. They realize that ADA programmed commands into the GD mainframe, to make the previous simulation "authentic" by actually realizing the events of the simulation, and then destroyed itself so the commands could not be overridden. Meanwhile, Zane helps Fargo connect with Holly in the mainframe, whose full consciousness had been trapped in the Matrix after her neural patterns were disconnected from her body. Zane develops an adaptive waveform forcefield to hide the Matrix and not repeat the events of the last episode. Fargo manages to get in a few minutes with Holly before being called out to supervise the actual disaster. Allison and Jo also must deal with the emotional awkwardness/trauma of the possibility of Jack winding up with Jo if Allison were gone. The final piece of the scenario is a missile attack that ADA launches from a nearby missile silo. When the EM shield does actually fail, Zane uses his adaptive waveform shield to stop the missiles from destroying GD and the town. Jack and Fargo set it up at the exact coordinates specified by Henry, and they successfully save the town at the last second. Later, everyone gets together at Cafe Diem to celebrate. After the cafe, Fargo goes back to the Matrix to face a hard reality and tell Holly that she is technically dead. This saddens Holly and the two hold each other for comfort wondering what is next.