San Francisco judge Catherine Lavinio places a frantic call to 911: there's an intruder in the house trying to kill her! As the 911 operators rush to dispatch a unit to the scene, the call is cut off, and Judge Lavinio is later found dead.

Meanwhile, Monk, Sharona and Benjy are enjoying a friendly game of Clue when a call comes in asking Monk to assist on the case. They arrive at the crime scene to find the house in complete disarray, as if hit by a tornado. Monk is slowly beginning to piece together clues when he's given some unbelievable news: the cops' prime suspect is 800-pound tycoon Dale J. Biederbeck III, a.k.a. "Dale The Whale." But Monk wonders how that can be possible - Biederbeck hasn't left his bed in eleven years, and can't even fit through his bedroom door!

When Monk goes to question Dale, it reopens some old wounds - seven years ago, Biederbeck was responsible for a devastating lawsuit that virtually bankrupted Monk and his wife Trudy. Now, years later, Monk is certain that Dale is behind the murder of Judge Lavinio, but the hard part will be proving it.

Monk and Sharona begin to follow the trail of clues in order to piece together the mystery. First, Monk meets with two little girls who witnessed the crime, and both swear they saw an 800-pound man inside Judge Lavinio's house. Then Sharona catches up with Dale's personal nurse in an ill-fated attempt to learn more about him.

Eventually, Monk is able to piece the riddle together: the murder was committed by Dale's personal physician, Dr. Christian Vezza, who wore a fat suit to disguise himself as Dale the Whale. By making sure all the clues pointed to Dale, Biederbeck and his doctor thought they would have an airtight alibi for their perfect crime - after all, Dale the Whale is the one man who couldn't possibly have committed the murder. But there was one thing they weren't counting on: the sleuthing ability of former San Francisco police detective Adrian Monk.