Sheldon reverts back to 2003 when he learns that Leonard and Penny are moving in together. Meanwhile Howard and Raj form a band to play at the comic book store.
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When Barry Kripke gives the guys fencing lessons, he makes a point of letting Sheldon know he's interested in dating Amy. Stuart has trouble getting female customers at the Comic Book Store, so Penny, Amy and Bernadette stop by to help out.
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A helium shortage leads Sheldon and Leonard to do business with a dealer in the black market in order to acquire some of the element for an experiment they need to complete.
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Sheldon's interview for a "Star Trek" documentary focusing on Spock turns up a shocking revelation about his breakup with Amy. Meanwhile, the Wolowitzes haggle over the remodeling of his family home.
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When Leonard, Penny and Bernadette learn that Amy is going out on a dinner date, the trio set out to spy on her and the guy. Meanwhile, Sheldon recruits Raj and Howard to find a woman for him.
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Now just friends, Sheldon and Amy spend Thanksgiving at the aquarium; a reluctant Wolowitz volunteers at a soup kitchen with Bernadette, Raj and Emily; and Penny realizes that Leonard knows a bit more about her than he's let on.
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Howard reconsiders entering into a legal partnership with Leonard and Sheldon regarding the patent for the infinite persistence gyroscope. Also, the women offer Raj dating advice after Emily reaches out to him following their breakup.
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Sheldon tries to teach the guys a lesson after they cut him out of a potentially valuable Bitcoin investment. Also, a seven-year-old video reveals a secret about Leonard and Penny's relationship.
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Sheldon and Amy try to eliminate stress from wedding planning by applying math to the process. Raj "breaks up" with Howard after realizing his best friend is actually hurting his confidence.
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Sheldon and Howard plan birthday celebrations for Amy and Halley, respectively. Leonard receives a Christmas letter from his brother that causes him to spiral out about his own lack of accomplishments.
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To discover who would be most qualified to be best man and maid of honor at their wedding, Sheldon and Amy subject their friends to a series of secret experiments. Also, Penny reveals her true feelings about Amy.
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When Sheldon kicks Amy out to work solo, she and Leonard bond during a series of science experiments. Bert replaces Howard in the band Footprints on the Moon, and Sheldon finds Penny a surprising source of scientific inspiration.
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