It is Christmas time in San Francisco, but all is not merry. A cop is dead after drinking a poisoned bottle of wine intended for Captain Stottlemeyer, and while all leads point to a man with a grudge against the Captain, Monk isn't convinced. With Natalie's help, Monk does some of his own detective work, which soon finds him caroling, fighting off crowds at the mall... and even doing some undercover work as a certain jolly, red-suited fellow. Will Monk solve the baffling crime in time to enjoy the holidays?