As the elderly residents of the Malden Retirement Home relax after dinner, just down the hall, Miles Holling, who is the world's oldest man and just one day shy of his 115th birthday, is being suffocated by a shadowy figure.
Captain Stottlemeyer's wife Karen, who once profiled Holling in a documentary film she made, suspects that the elderly man's death was no accident. But Captain Stottlemeyer, citing Holling's age, believes he likely died of natural causes. Monk is brought in to settle the dispute, and he agrees with Karen - among other clues, Holling's walker was found in the center of the room, and he couldn't have reached the bed where he was found dead without it.
The dispute between Stottlemeyer and his wife eventually gets him kicked out of his house and lands him as Monk's unwanted houseguest. To add to his problems, Stottlemeyer still can't get his only unsolved case, the hit-and-run death of a man named Darren Leveroni five years ago, out of his head.
Monk and Stottlemeyer are probably the most mismatched roommates in history, and they are soon at each other's throats. Things eventually get so bad between them that Stottlemeyer decides he has to go home immediately and beg for his wife's forgiveness. But Monk reminds Stottlemeyer that she's not likely to take him back until he finally watches her incredibly bad documentary on Holling, a task that Stottlemeyer has been avoiding for quite a while.
In the video is footage of a time capsule dedication ceremony, in which a small town mayor invites everyone, including deputy mayor Dennis Gammill, onto the podium to drop a message in for future generations. After the notes are dropped in, the mayor unexpectedly announces that he plans to dig up the capsule in just five years if Holling is still alive. Stottlemeyer notices one other thing: Gammill drove to the ceremony in a rental car.
With that, Stottlemeyer is able to utter the words he's been waiting to say to Monk for years: "I solved the case." What Stottlemeyer realizes is that deputy mayor Gammill rented a car that day because his own car was involved in the Darren Leveroni hit-and-run case. His guilt was overwhelming, so he put a confession into the time capsule, but when Gammill realized that the capsule - and the confession - would reemerge if Holling lived to see his 115th birthday, Gammill was forced to kill him.
For once, it is Stottlemeyer and not Monk who solves the case, thus ending a cold streak that began five years earlier.