Sheldon struggles to understand what is going on with Amy; Penny must decide if she can get past Leonard's bad behaviour.
Leonard tries to ease Penny's mind; Sheldon plans a special episode of Fun With Flags; Bernadette feels bad about keeping a secret.
A flat tire during Leonard's bachelor party weekend in Mexico puts the guys' skills to the test. Penny is compelled to tell her family that she and Leonard eloped.
An impending change to his living arrangements inspires Sheldon to revert to 2003, before he met Penny and Leonard; Raj and Howard form a band.
Barry Kripke expresses interest in Amy while leading a fencing lesson for the guys; when Stuart tries to attract female customers to the store, Penny, Amy and Bernadette help out.
Leonard and Sheldon go to great lengths to secure the helium they need during a nation-wide shortage; Bernadette and Penny try to to find Amy a new man on a dating app.
Jim Parsons
Sheldon Cooper
Sara Gilbert
Leslie Winkle
Kaley Cuoco
Penny/Penny Hofstadter
Simon Helberg
Howard Wolowitz
Kunal Nayyar
Raj Koothrappali
