Howard receives some shocking news as everyone prepares for the re-opening of the comic book store. Meanwhile, Penny tries to teach Sheldon how to "let it go," but can't follow her own advice when she learns something infuriating about Amy.
Sheldon and Penny agree to participate in an unusual experiment. Leonard, Amy, Raj and Emily spend the evening trying to escape a room with a "zombie". Howard and Bernadette run into trouble at the airport after returning from Mrs. Wolowitz's funeral.
A trip to the pet store ends in a fight after Amy learns Sheldon has applied for a one-way mission to colonize Mars. Meanwhile, Leonard surprises Penny with a very "adult" purchase, and Raj gets into trouble when he snoops around Emily's apartment.
When Leonard and Sheldon are invited to speak at UC Berkeley, they take a detour to try and meet one of their idols. Meanwhile, while cleaning out Mrs. Wolowitz's house, a ping pong battle ensues when Howard and Bernadette argue over the fate of his TARDIS.
Howard questions his engineering abilities when he and Sheldon can't get a toy drone to fly. A cancelled flight nearly prevents Leonard from giving the commencement address at his former high school. Raj pits his parents against each other when his father cuts him off financially.
As Sheldon presses Leonard and Penny to set a wedding date, he encounters major changes in his relationship with Amy. Meanwhile, Raj wonders if he should break up with Emily, and Howard and Bernadette struggle to ask Stuart to move out.
Penny struggles with Leonard's confession that he kissed another woman as they prepare to get married in Las Vegas. Meanwhile, Sheldon doesn't know what to do after Amy pushes pause on their relationship.
Leonard and Penny try to work through their marital issues. Meanwhile, Sheldon films a special episode of "Fun with Flags" after his breakup with Amy, and Bernadette feels guilty about withholding a secret from Penny.
Wil Wheaton interviews Sheldon for a Star Trek documentary where he reveals the ring and his plan to propose to Amy. Bernadette wants to start renovating the house and the topic of starting a family together with Howard is brought up.
On Thanksgiving, Sheldon and Amy try to spend time together as friends and go to an aquarium, Howard reluctantly agrees to volunteer at the soup kitchen with Bernadette, Raj and Emily, and Penny discovers that Leonard knows more about her than she thought.
Sheldon has a revelation when he realizes why a song was stuck in his head. Meanwhile, Amy invites Dave over for dinner despite their previously awkward date, and Howard and Raj become obsessed with a fan of their band.