After failing to win back his girlfriend, Ellen, in Summit, New Jersey, Monk returns to San Francisco, where he is surprised to find that another relationship has taken a new turn. Natalie decided to make things official by setting up an office for Monk and Teeger, Consulting Detectives. With Monk's typical response to change of any kind, they have more than a few wrinkles to iron out of their new routine. But when Lieutenant Amy Devlin comes to them for help, it's time to stop bickering and get to work. A disgruntled employee of a small import business, Wyatt Noone came into work one day and started shooting, killing three coworkers and leaving a female hostage severly wounded. Spotting Wyatt through the office windows, the police surrounded the building, but he still managed to disappear, leaving Lieutenant Devlin with a messy and baffling mystery on her hands. Visiting the bedridden survivor, Sarabeth Winslow, Monk finds her to be helpful, cooperative, and, now that he's on the rebound from Ellen, quite charming as well. But as he and Natalie try to track down Sarabeth's assailant, they discover that Wyatt has left behind barely a trace of his past, almost as if he managed to disappear from existence altogether.