Known for having an amazing attention to detail, and a way of piecing these details of a crime together to solve the case, Adrian Monk (Tony Shalhoub) was San Francisco's top detective, solving some of the most baffling cases.  Monk's late wife Trudy was a reporter killed mysteriously by a car bomb.  This devastating moment in Monk's life left him with obsessive-compulsive disorder, a psychological disorder that caused him to develop fears of just about everything, from germs, heights, crowds, and even milk.  The disorder creates a difficult life for Adrian and led him to lose his job.

Adrian, who is now called in as a private consultant, has assistance from his personal nurse Sharona Fleming (Bitty Schram), and his psychiatrist Dr. Kroeger (Stanley Kamel).  With their help, Adrian hopes to return to the police force and try to live life with fewer worries.  Sharona has also helped out with cases, becoming Monk's own "Girl Friday," an unlikely Dr. Watson to his Sherlock Holmes.

Captain Leland Stottlemeyer (Ted Levine), Monk's former boss, calls him in on some of the department's toughest cases.  Though tired of being shown up by Monk, he appreciates the help, and hopes one day he can see Monk return to duty.

Always there to boost his commander’s ego is Lieutenant Randall Disher (Jason Gray-Stanford) who serves as the captains “sidekick.”