The Platonic Permutation

"The Platonic Permutation" is the ninth episode of the ninth season of The Big Bang Theory. The 192nd episode overall, it first aired on CBS on November 19, 2015. The story follows the characters throughout Thanksgiving. The first storyline explores Sheldon and Amy's relationship as they meet-up, after being broken up. The next subplot follows Bernadette, Raj, Emily and Howard where they volunteer at a soup kitchen and the last follows Leonard and Penny after they have a minor conflict as Penny forgets Leonard's birthday.

"The Platonic Permutation" features a guest appearance of South-African American entrepreneur and business magnate, Elon Musk as himself. Critics had mixed reviews of the episode. Critics praised Sheldon and Amy's storyline, but were critical of the other two subplots and Musk's appearance.