Season 8, Episode 20-"The Fortification Implementation" - Howard discovers he has a half-brother; Sheldon and Amy build a blanket fort in the apartment and intend to have a platonic sleepover; and Leonard gets a surprise when he learns Penny's been invited to audition for a Kevin Smith movie.
Season 1, Episode 22-"The Graduation Transmission" - Leonard's high-school alma mater asks him to make a graduation speech, but plans may be scuttled when his flight is canceled. Meanwhile, Raj's allowance is canceled by his father.
Season 09, Episode 02 – “The Separation Oscillation”
To ease Penny’s mind, Leonard pays a visit to the woman he kissed during his expedition to the North Sea, while Sheldon’s breakup with Amy leads him to retaliate by shooting a special episode of “Fun With Flags.” Later, Bernadette is wracked with guilt over withholding a secret from Penny.
Season 09, Episode 04 – “The 2003 Approximation”
Sheldon learns of an impending change in his living arrangements and decides to revert back to 2003, a simpler time before he met Leonard and Penny. Also, Howard and Raj form a band to play at the Comic Book Store.