Harry Orwell awakens one morning and finds a young girl, Liberty Cole, sleeping on his beached boat. Harry goes out for his morning jog thinking he's sent her on her way. When he returns and finds she's still there, he calls the department and begins checking on who she is.
He is later contacted by his friend on the force, Humphrey Kenner, when Charlie English, Kenner's son-in-law, is found shot to death. Harry checks the crime scene and renews acquaintences with Milt Bosworth, whom he knew when he was on the force. Harry goes to reveal the news of English's death to his estranged wife, Jennifer, a model who is emotionally unstable due to her relationship with the abusive Charlie. Jennifer is now seeing John Lockport, a former Army colonel, and Kenner wants Harry to help protect Jennifer and help prove Lockport innocent, as he is the prime suspect in Charlie English's murder due both to motive and to the fact a gun in his ownership is now missing.
Harry talks to Jennifer and she reveals that car keys and other items on her person frequently turn up missing. Harry gets permission to check her apartment, but when he gets there he confronts Roy St. John, a deranged photographer who has been tailing Jenny and lives in an apartment house up the hill from John Lockport's place. Roy stabs Harry with a fork and fires a shot from Lockport's gun, then escapes. Harry digs out the slug and has it sent to ballistics, now confident John Lockport is innocent, but later he gets word that Lockport is found dead at his house, having started a note saying "I am guilty."
Bosworth believes it an open-and-shut endgame of a murder-suicide, but Harry sees the note is unfinished and telephones ballistics on the slug from Jenny's apartment - it matches the slug that killed Charlie English. Before he can find and inform Jenny, he finishes up his separate investigation that finds the mother of Liberty Cole, in jail for shoplifting; Harry has the woman cleared and reunites her with her daughter.
Jenny, meanwhile, is shopping and is met by Roy, unaware of who he is; he gives her a folder of pictures of her after revealing he is a photographer. At her place she admires the photos before Harry tells her that Lockport is dead. Jenny flies into a grieving rage and collapses onto her bed with Harry - seen by Roy from outside. Concluding Harry and Jenny are lovers - and unaware that Harry has in fact fallen in love with Jenny - Roy vows to "purify" Jenny.
Harry, seeing the photos Jenny received, deduces who took them, arranges for a policeman to guard Jenny, and checks out Lockport's apartment again; it is here he finds Roy's apartment, but Roy has recorded a lengthy missive about "purifying" Jenny, then kills the policeman guarding her apartment, kidnaps Jenny, forces her to put on a white dress, and takes her to the top of a building under construction. Harry finds the recorder Roy left and plays it to Kenner, and leads the chase to the building where the deranged photographer and the terrified object of his obsession are straddling the edge of its top floor.