Sharona's sister, Gail, is starring in a play bound for New York, and Monk and Sharona are in the audience. During a scene, Gail uses a fake knife to "stab" another actor. The actor gasps and wheezes before falling to the floor - but then doesn't get up. A doctor rushes onstage from the audience and determines that the actor was stabbed in the chest. Gail is immediately arrested and charged with murder.
As if things weren't stressful enough for Sharona, her mother arrives for a visit. Sharona tries to push aside her feelings to prepare her mother for the news of Gail's arrest. As expected, Mrs. Fleming is beside herself - her daughter is being accused of murder! She asks Monk and Sharona to help clear her daughter's name.
Monk and Sharona head back to the theatre to investigate. While questioning everyone involved with the play, Monk learns that Hal Duncan suffered from a severe food allergy. This and other details start pointing towards Gail's understudy, Jenna Ryan, as the most likely suspect.
Monk and Sharona tail Jenna to a singles "speed dating" event, where Monk has no choice but to sign up in order to question her. The speed dates don't go very well for Monk. When he's at last paired up with Jenna, his inquisitiveness puts her on the defensive. Growing suspicious of Monk's questions, she refuses to talk about the stabbing.
When Monk and Sharona arrive back at the theatre, they decide to "recreate" the fatal moment in the play. The director witnesses their display, and insists on casting Monk as the victim's temporary replacement. Despite his fears, Monk reluctantly agrees to do it in order to get closer to Jenna. Monk is going to be an actor!
Right before his theatrical debut, Monk starts replaying the events of the night of the murder. But as he's about to go on, he is suddenly stricken with stage fright! As Sharona begins checking his pulse, it hits him. Monk has solved the case.
Monk goes out on stage. He's scared. He can barely get through his lines. Then, as the infamous knife scene approaches, Jenna brandishes a real knife instead of the prop knife! Sharona rushes the stage and struggles to disarm Jenna, and Jenna gets knocked out during the struggle. A man in the audience calls out for a doctor. Monk recognizes him from the previous performance - he was the doctor who pronounced Hal Duncan dead.
Monk then reveals that the man from the audience is actually Jenna Ryan's father! Together, they concocted a plan to frame Gail for murder so Jenna could take over the lead role. Knowing about the victim's severe allergies, Jenna spiked the apple Hal eats in their scene with peanut oil. When Hal collapsed, Jenna's father raced to the stage posing as a doctor. During all the commotion, he removed the retractable prop knife attached to Hal's shirt and administered the fatal stabbing without being noticed. The motive? A father's blind love for his daughter - and a daughter's over-ambitious drive for success at any cost.