Lt. Eve Dallas is dreading going to a fancy dinner with her fantabulously wealthy husband Roarke and some of his business associates when she is called to a grisly crime scene. A low level drug dealer took a baseball bat to his neighbours when they tried to make him turn his music down, and while the cop on the scene only tried to stun him, the assailant fell down dead. On his computer screen the cops on the scene find the message: "Absolute purity achieved."
A couple of days later, one of the computer division cops working with the computer in question goes absolutely apeshit and starts firing wildly at his colleagues, hitting Detective McNab in the process and locking himself in an office with his superior (and Eve's mentor and former partner) Captain Feeney as a hostage. Eve, realizing that he seems to be suffering from the same mysterious rage as the dead drug dealer, manages to save Feeney, but is unable to calm her crazed colleague before he collapses and dies. It's clear that they're dealing with some form of virus that can spread from computer to person, and that it kills in a most unpleasant way.
When the group known as the Purity Seekers publicly announces that they mean to bring purity to New York by killing those who prey on children and the weak, Eve has to try to solve the murders of victims no one will miss, and track down an organization whose goals are seen as admirable to many of the people she's sworn to protect.
Jamie Lingstrom, the technology whiz kid from Ceremony in Death makes a return appearance, and Mavis (Eve's best friend and famous rock star) surprises Eve with some unexpected news that completely stuns the emotionally troubled lieutenant. The entire cast of regulars have to deal with the difficult knowledge that McNab may be permanently wheelchair-bound after his accident, which obviously hits Peabody especially hard, and Eve has to realize that sometimes she and Roarke do not agree on how justice should be served to criminals. Another entertaining installment, but without any huge developments on the character front.