Dwight tells Angela to delete all her sensitive emails, leading Pam and Jim to speculate that they may be hooking up. Pam spots Angela buying two Baby Ruth bars and she sees Dwight eating one later.
Jim sends out an e-vite to all the employees for a barbeque he's having at his house that night. Michael happens upon the invite while spying on Jim's email and notices he's the only person not invited.
Jim didn't invite Michael because he didn't think people would be able to relax and have fun. He tells Dwight it's a surprise party for Michael, so as not to let the cat out of the bag.
At the end of the day, everyone avoids Michael on their way out so they don't have to tell him about the party. Michael asks Jim what he's doing and Jim says he has plans. Michael tells Jim he also has plans - improv class.
Michael goes to improv class. Except he only incorporates one character in his routines - a man who always has a gun. His improv teacher makes him put the guns away. At the end of class, everyone else heads off for drinks, excluding Michael for the second time in one day.
Jim's party is fun and casual. Karaoke time is just getting started when Michael suddenly shows up. He takes over the karaoke mic and the party literally comes to a screeching halt. Jim is pissed that Michael crashed his party, but he sucks it up and joins him on the mic in order to salvage a good time.
The camera catches Dwight and Angela making out in a back room.