Working as a private investigator, Monk visits a crime scene to investigate the murder of Nicole Vasquez. He finds a number of significant clues, but is not yet sure of the identity of the murderer. Later, shots ring out at a campaign rally, and San Francisco mayoral candidate Warren St. Clair's bodyguard is killed. The incumbent mayor instructs Captain Stottlemeyer to bring Monk in on the case, and reluctantly, he does.
After a brief meeting with Warren St. Clair, his wife Miranda, and their aide Gavin Lloyd, Monk goes to the scene of the assassination attempt. While there, he unexpectedly discovers a thin link between the attempt on St. Clair's life and the murder of Nicole Vasquez: Nicole was briefly a volunteer for the St. Clair campaign. This lead brings him to St. Clair campaign headquarters, where Monk questions one of the current volunteers about Vasquez. When that volunteer later turns up dead, Monk's suspicion about a connection between the Vasquez and St. Clair cases grows even stronger.
Sharona begins to suspect that St. Clair's wife Miranda ordered a hit on her husband, a theory bolstered by the fact that St. Clair is worth $150 million. But Monk has other suspicions - including that Miranda and another one of St. Clair's assistants have been carrying on an affair.
It isn't until watching a news report on the assassination attempt that the pieces begin to click together in Monk's mind. Monk reassembles everyone at the site of the campaign rally in order to recreate what happened that day. He explains that the assassin wasn't even trying to kill Warren St. Clair: he was actually hired to kill the bodyguard. Why? Because the bodyguard was the first person St. Clair aide Gavin Lloyd approached about murdering Nicole Vasquez - who had discovered that Lloyd was embezzling campaign funds while she was still working as a St. Clair volunteer. When the bodyguard refused to carry out the murder, he had to be silenced.
To prove his theory, Monk exhibits a newspaper photograph taken at the rally. It shows Lloyd pointing in the direction of the shooter just after the shots were fired. But as Monk proves during his recreation, Lloyd's sight line was obscured, and the echo of the gunshot off of the surrounding buildings would have masked the direction of the shot. There was no way Lloyd could have known where the shots were coming from - unless he was the one who ordered the hit and knew where the gunman would be. Once again, the obsessive-compulsive detective solves an unsolvable case.