The Sentinel (1974) is a novel written by Jeffrey Konvitz.
Alison Parker, a beautiful but troubled fashion model moves into a gorgeous New York City brownstone house that has been divided into apartments. The house is inhabited on the top floor by Father Francis Matthew Halloran, a reclusive blind Catholic priest who spends all of his time sitting at his open window.
Alison is romantically involved with Michael Lerman, a private lawyer and former prosecutor. It soon becomes apparent that Alison's life is beset for a number of reasons. She had a horrible relationship with her recently deceased father, and has narrowly survived at least one suicide attempt. Michael himself is under suspicion in the death of his former wife. A determined New York City Police Department detective named Gatz is sure that Michael murdered his wife, and soon comes to suspect Alison as well.
Hoping to leave her problems behind her, Alison finds that they've worsened. She suffers sleep loss, horrible nightmares involving her father and soon begins to find herself suffering blinding headaches.
Looking for some distraction, she tries to ingratiate herself with the building's other occupants - but finds that they are bizarrely eccentric and obnoxious. Alison complains about her neighbors to the building's real estate agent. The agent is confused, telling a shocked Alison that there are no neighbors - besides for herself and Fr. Halloran, no one else lives there.
Looking for answers, Michael breaks into a records archive of the Catholic Church. Researching the past of Fr. Halloran, Michael learns that the man has none. Rather Halloran's life "began", to the day, that another man's life apparently came to an end, leading Michael to believe that the two men are one and the same. He also finds similar records for a woman, a nun named Sister Therese who is to reside in Alison's building. Michael soon concludes that Sister Therese is actually the woman that Alison is meant to become.
Rushing to Alison's building, he confronts the blind priest, only to be killed. Returning to the building, her headaches returned and her skin beginning to desiccate, Alison finds Michael seemingly unhurt. He reveals that he is actually dead and also damned for killing his wife. He also explains that the house is actually positioned over the gateway between our world and Hell and that there must be gatekeeper to protect the world from the denizens of the underworld. Until now, that gatekeeper, or sentinel, had been Father Halloran, but Alison is now expected to succeed him. Her troubled past, especially her suicide attempt, make her the appropriate choice. The inhabitants of Hell are actually her fellow "neighbors", and they know that they have one chance to escape the abyss - pressuring Alison to complete her suicide. At the last minute, Father Halloran appears and saves Alison, driving the "neighbors" back to hell.
The book ends with Alison becoming the new sentinel.
A sequel titled The Guardian followed.
See The Sentinel (film) It was written by Konvitz also.