Andy and Tracy Safian are a newlywed couple living in a Victorian house that they are restoring in Western Massachusetts. He is an Associate Dean at a local college, while his wife teaches art to children. When a student is attacked and seriously wounded by a serial rapist, Dr. Jed Hill, a brilliant surgeon who has recently joined the staff of the area hospital, operates and saves her life. Money is tight, so Andy invites him to rent the third floor of their home, in order to finance the new plumbing. With his propensity to bring home sexual partners and to party late into the night, Jed quickly proves himself to be a less-than-ideal tenant.
When Paula Bell, one of Andy's students, is attacked and killed by the serial rapist, Andy is the one to find her body, prompting police detective Dana Harris to view him as a possible suspect. Harris asks Andy to come to the police station and submit a semen sample in order to clear his name. While at the police station, Andy learns that Tracy has been hospitalized and is being operated on by Jed. In removing one of Tracy's ovaries, which has ruptured due to a cyst, Jed discovers Tracy is pregnant, but the stress of the procedure causes the fetus to abort.
Another doctor notices that Tracy's other ovary is torsed and appears necrotic. Jed consults with Andy and advises him to agree to the removal of Tracy's second ovary, rather than risk her life. Andy painfully agrees, since this will mean that Tracy can never have children. Jed overrules the protests of other doctors that the ovary might still be healthy and he removes it. After the removal, it is confirmed that the ovary was, in fact, healthy. Tracy tells Jed she's suing him for malpractice.
Jed delivers a deposition in which he launches into a monologue about his own infallibility as a surgeon, concluding with the assertion that he is literally God. Fearful of the negative publicity that would result from a civil trial, the hospital and Jed's insurance company settle with Andy and Tracy for $20 million. However, Tracy leaves Andy, telling him that she can't forgive him for the loss of her ability to have children.
The serial rapist, a handyman named Earl, is arrested, clearing Andy's name. In the aftermath of the arrest, Dana informs Andy that his semen sample indicated that he was sterile, and that he couldn't have fathered Tracy's child. Andy confronts Tracy's lawyer, Dennis Riley, accusing him of having impregnated Tracy; Riley protests his innocence, but tells Andy that Tracy's mother — whom she had told Andy had died 12 years ago — can answer all of his questions. Riley refuses to break lawyer-client privilege, but tells Andy to take a bottle of Scotch to her.
Andy tracks down Mrs. Kennsinger, who tells Andy that Tracy is a lifelong con artist. As a younger woman, she had an affair with a wealthy man, who paid for her to have an abortion; Tracy kept the money and had it done at a clinic, beginning her career as a con woman. Andy ultimately learns that Tracy arranged for Jed to move into the house so that he could begin overdosing her with a fertility drug which causes ovarian cysts when taken in excess amounts, revealing the real reason why Tracy left Andy for Jed. An angry Andy confronts Tracy and tells her he wants half of the settlement money. Suspecting that she might try to murder him, Andy implies their next-door neighbor, the ten-year-old boy who's been their seeming voyeur, is named in his will as a potential police witness to her and Jed's nefarious activities.
Supported by Andy's suggestion, Jed tells Tracy to give Andy what he wants so they can leave the country, but Tracy instead suggests murdering the boy. Jed refuses to kill a child, so Tracy, fed up with Jed's abusive attitude, shoots him to death, ending their partnership. That night, with the money about to be given to Andy, she slips into the neighbor's house and attempts to suffocate the boy, only to see that the figure she had seen sitting by his bedroom window was in fact a CPR dummy. Tracy destroys the dummy and lunges at Andy, claiming that it was a set-up. Detective Harris appears and arrests her, revealing that the boy's supposed agreement to testify against her was part of a sting operation to catch her in the act of attempted murder.
As Tracy is led away in handcuffs, the real boy and his mother return home; as she is put into the police car, Tracy sees that the boy is, in fact, blind. Andy leaves with Dana to have a drink of Scotch.