Boston-based private detective Spenser goes to work for a conservative senatorial candidate named Meade Alexander, allegedly to protect him from some vague threats he has received. However, Meade reveals that Spenser will be investigating a blackmail tape showing Ronni, Meade's wife, having an affair with an anonymous man. Meade's opponent in the political race, Robert Browne, is high on Spenser's suspect list because Browne is on the payroll of Boston mafioso Joe Broz, who does not want to see his politician get beaten by a conservative whose wife has been indiscreet. Spenser empathizes with Meade, whose only wish is to protect the woman he loves.

Spenser begins by investigating some threats made against the Alexander campaign by one Sal Pelletier, a cheap thug hired in Springfield by Vinnie Morris, Joe Broz's first lieutenant. While Spenser's clues seem to point to Joe Broz, Spenser believes that the blackmail is too subtle and careful to have been perpetrated by the brutish mob leader. Once the detective hits that dead end, he requests to see the pornographic video of Ronni Alexander. He flies to Washington DC to see the video in the Alexander's home in Georgetown. There he gathers a few clues from the video, but does not know where to turn to next.

While in Washington, Spenser spends time with Susan, his long-distance girlfriend without whom the detective is miserable. Susan calmly insists that she stay in DC, and Spenser has no choice but to rethink his definition of love and rediscover how best to love this woman. While working the case the next day, he recognizes the logo of Georgetown University from Ronni's video, and remembers that Joe Broz's son attends Georgetown. Spenser breaks into Gerry Broz's apartment and immediately recognizes the apartment from the blackmail tape.

Spenser tails Broz as he makes several stops at private homes the next day, then watches as two underage girls arrive at Broz's apartment and then leave several hours later, obviously intoxicated. Spenser stops one of the girls and impersonates a police officer, and the girl confesses that Broz sells cocaine and often trades the drugs for sex. She also reveals that Broz hosts what he calls "granny parties", orgies between local housewives and his college friends. At the next "granny party", the girl sneaks Spenser in and he takes several photographs. Using those photographs to convince one of the women who participated in the orgy, Spenser confirms what the girl confessed to him.

The next day Spenser is taken to a meeting with Robert Browne, who demands that the detective stop harassing Gerry Broz. Spenser realizes that if Browne is protecting Gerry, then Joe Broz must not know about his son's extracurricular activities. Spenser flies back to Boston and meets with Broz and Vinnie Morris, offering to bury the entire escapade if they will merely destroy the blackmail tapes. Broz arranges a hit on Spenser, which Spenser survives with a bullet wound in his leg.

Spenser, joined by fellow enforcer Hawk, makes a deal with Broz to compromise: Broz will destroy the tapes, and Spenser will not hunt him down for trying to have him killed. Spenser and Susan reunite and reach a tentative peace when Spenser tells Susan that no matter what she has to do to find herself, he will always love her.