Immortal in Death (1996) is the third book of the In Death series by J. D. Robb, following Glory in Death and preceding Rapture in Death.
The story starts with Eve Dallas worrying about getting married to Roarke. Still at home, she tells Roarke and that she is going shopping for a wedding dress. She tells him that she is getting the dress with her own money. She makes her way to Leonardo's and just looking at the bright dresses in the window she wants to turn back, but encounters her friend Mavis who drags her in. Once inside, Leonardo studies Eve in such a way as to get an idea of the perfect dress for her. He settles on a bronze colour which Eve agrees to.
He tells her to undress - for measurements, not for prurient reasons. Mavis leaves them to it and as Eve warns Leonardo not to hurt Mavis, another woman, Pandora, comes in and attacks Leonardo. Unable to stop her, Eve decks her and she falls to the floor. Eve is starting to get dressed when Mavis comes in, and then both women are on the floor. Leonardo and Eve break them up and Pandora threatens them, then leaves. Mavis tells Leonardo that because she loves him, she'll go away so that he can have a future.
Eve leaves Leonardo's and returns home exhausted. She makes her way to the bedroom and lies face down on the bed. Roarke finds her and lies down beside her as she explains what happened. Roarke tells her he'll be going away for a while, as he rolls her over and unbuttons her shirt. She asks him how long but soon gets distracted and they make love.
The next morning, Eve visits the morgue and discovers that Carter Johannsen (alias Boomer), one of her informants, was brutally beaten to death with a blunt instrument and thrown in the river. She enlists the help of Officer Peabody and Captain Feeney to track down the killer. With Peabody, Eve visits Boomer's flop which is devastatingly filthy. They go through his entire home and find a sample of a drug, along with its formula, under his bed.
Eve goes home to Roarke and tells him about what she and Peabody found. Showing him the formula, they discover it is a new type of drug, not yet released, that can both enhance sexual performance and act as a cell regenerator that restores youth.
Eve falls asleep exhausted and stressed out. However, in the middle of the night, Mavis calls Eve to come over to Leonardo's because someone's dead. Eve scurries over to his place and finds Pandora dead, with her face beaten to a pulp.
An investigation is made into Pandora's death, and throughout, all the evidence points to Mavis. In fact, so much evidence points to her that it seems as if she were framed. Eve learns that Mavis went to see Leonardo because she just couldn't stay away from him any longer. Tracking down Leonardo, she finally finds him at Mavis' place, drunk and bleeding from accidentally falling on his glass. Believing that neither Mavis nor Leonardo could have committed the crime, Eve sets off to find the true killer.