David Moore, a wealthy Manhattanite, comes rushing into the lobby of his apartment building, carrying his comatose wife Joan in his arms. In the hospital, Joan Moore is diagnosed as suffering from insulin shock, even though she is not a diabetic. On further investigation, Green and Briscoe find out that Joan is actually suffering from Parkinson's disease—and, unbeknownst to her husband, has been receiving treatment from Dr. Richard Shipman—and suspect that her husband is either attempting to kill her or helping her commit suicide.
Trying to trace the source of the insulin, the detectives run into the psychiatrist Bertrand Stokes, who has previously smuggled that substance into the country. Stokes' wife, however, explains that the insulin is part of a sex game in which a number of men inject their wives with insulin, have intercourse with them, tape the entire event, and swap the tapes among each other. David Moore admits that this is indeed happening, but claims he kept it from the police in order to spare his wife the embarrassment. Because he is accused of murdering Joan, David loses custody of her (and her fortune) to Joan's daughter, Debbie Mann.
On further investigation, it turns out that Joan's Parkinson's disease is not natural, but induced by the drug MPTP. Remnants of this drug are subsequently found in Debbie's office, and it turns out that her company is on the brink of bankruptcy and is only kept afloat by an infusion of Joan's money. Green and Briscoe find out that Debbie and Shipman, who previously did research on MPTP, know each other and get Debbie to confess that the two conspired to slowly poison Joan. However, Debbie claims she pulled out of the arrangement at the last minute and that Shipman administered the fatal dosage of MPTP on his own. With the threat of reviving Joan through the drug L-dopa, Shipman finally confesses that this scenario is indeed true.