Sheldon and Amy get engaged. Howard and Bernadette meet Howard's half- brother Sam Wolowitz.
Leonard and Bernadette are working together in their lab, while Bernadette is thinking on how to find a way to tell Leonard about how Sam Wolowitz suddenly showed up, but then she simply says it quickly and starts crying with happiness so Leonard comforts her with a hug. Howard is in his lab and then Raj passes by and then Howard tells him about Sam showing up quickly like that. Sheldon and Amy are on Skype chatting about setting a wedding date and decide to make it 6 months from now. Back in their lab, Leonard is helping Bernadette feel okay and then they continue working and Penny passes by, but is surprised that a lot of tissues are in the trash so when asked why, Bernadette tells her about Sam showing up suddenly at the Wolowitz house. Penny reveals that she finally passed her first exam and even knows more then Bernadette about experimental physics. Later, Kripke meets up with Alex so she can help him find out exactly how Sheldon found his idea towards proving the Big Bang Theory. She then goes to Sheldon and tells him but then he invites her to help him instead of helping Kripke, and she accepts. Later, in the comic book store Emily is surveying costumers so she can help Stuart renovate the comic book store alongside Penny, Bernadette, and Amy. Later in 4A, Bernadette and Leonard are working together and then Leonard gives Bernadette the perfect way to master experimental physics so together they can prove the theory, and she agrees to do so since Penny is taking the exact class. She then starts talking to him about Sam and decides to say it to people one by one. Howard then enters 4A and is surprised that Bernadette is working late in 4A, but then she tells him that she told Leonard about Sam, and Leonard helped her take a class with Penny in Cal Tech. Howard is surprised and then Sheldon comes out of his bedroom with Alex who was working with him in beating Kripke in their ideas, the two are surprised to hear about Sam Wolowitz, then they all decide to tell Penny and Amy. Later in 4A in dinner, Leonard, Howard, Raj, Penny, Bernadette, And Emily are eating while Amy and Sheldon walk into the apartment together and announce their engagement.