The Large Hadron Collision
Leonard can only bring one guest on a trip to see CERN's Large Hadron Collider (the world's largest and highest energy particle accelerator) in Switzerland on Valentine's Day.
The Maternal Capacitance
Leonard and Penny are drawn together after a disastrous visit from Leonard's mother.
The Pork Chop Indeterminacy
The rest of the gang fall for Sheldon's twin sister, and Leonard's plan to win her heart is derailed when Sheldon declares he'll be the one to decide who can date her.
The Deep End
When Mabel befriends a cute merman trapped in the public pool, she's determined to help him out. Meanwhile, Dipper decides to volunteer as a lifeguard to see Wendy.
Go
As the wildfire approaches, everyone must evacuate. Nancy tells her family to pack up, while Conrad and Heylia must say goodbye to the growhouse. The authorities question Sullivan and Celia, while Shane continues to ask Nancy about Pittsburgh. As Andy deals at the evacuation center, Silas realizes the truth about Tara.