It's a great day for Capt. Stottlemeyer and Lieutenant Disher as they arrest a most-wanted criminal named Miguel Escobar after a dangerous chase through the streets of San Francisco. The arrest gets major media attention for the Captain, but it also draws the attention of the federal government, who order Stottlemeyer to hand over custody of Escobar. Stottlemeyer reluctantly agrees.
While things are going well for Stottlemeyer, Monk receives some bad news: he's been called for jury duty. Monk loathes the idea of being stuck in a room with eleven other people, but he has no choice when he's selected as a juror in a minor robbery trial. When time comes for the jury to deliberate, everyone votes "guilty" except for Monk. It's eleven against one, but Monk is sure that the defendant is innocent.
While Monk tries to win over his fellow jurors by picking apart the evidence, he looks out the window of the jury room and begins to suspect that there is a dead body in a garbage dumpster near the courthouse. Monk gets Stottlemeyer and Disher to check it out, and sure enough, there's a dead woman's body in the dumpster!
Monk begins tracking the murder investigation outside the window while simultaneously dissecting the robbery trial with his fellow jurors. Monk quickly determines that the dead woman in the dumpster was a member of the jury pool. Meanwhile, he slowly but surely convinces his fellow jurors that the defendant in the robbery case was innocent. When Monk finally convinces the last hold-out to vote "not guilty", a strange thing happens: Juror Number Twelve, a woman who had been one of the first to support Monk, suddenly changes her vote to "guilty." It doesn't take long for Monk to figure out what's going on: Juror Number Twelve killed the woman in the dumpster.
Here's what happened: Juror Number Twelve is Miguel Escobar's girlfriend. Stottlemeyer and Disher are soon to be handing over Escobar to the feds in the very courthouse where the robbery trial is taking place. Number Twelve needed to get on a jury to gain access to the courthouse so she could help Escobar escape during his transfer of custody, which is about to take place. Days ago, Number Twelve spotted the woman from the dumpster in the assembly room, killed her, and got on a jury using the victim's identity. Once on a jury, Number Twelve needed to keep the jury deliberating until the time came for Escobar to arrive at the courthouse.
Unfortunately, that time has come, and Juror Number Twelve has pulled out a gun. She ties up and gags all the jurors, overcomes the bailiff, and intercepts Escobar on his way up the courthouse elevator. She shoots two federal agents, and she and Escobar try to escape via a garbage chute on one of the courthouse's upper floors. Fortunately, Natalie suspects something is wrong in the jury room, and rushes there to untie Monk, who quickly figures out the escape plan and alerts Stottlemeyer. Escobar and his girlfriend are nabbed by the police, and Monk has more than fulfilled his commitment to jury duty.