Laura Spencer

Raj is wracked with guilt about dating Lucy and Emily at the same time, and Penny wrestles with her conscience over whether to accept a role in a terrible horror film.

After arguing with Sheldon, Howard tries to make amends by taking him to NASA headquarters in Houston; Penny has second thoughts about quitting her waitressing job when her car dies.

Sheldon faces a personal crisis when he starts to wonder whether he's wasting his time with his study of string theory, although Penny does her best to offer him advice.

When Sheldon tries to be spontaneous, it leads to unexpected friction between Penny, Amy and Bernadette.

A bad day compels Penny to re-evaluate her choices, including Leonard. Meanwhile, Bernadette and Howard must care for Mrs Wolowitz, and Sheldon gives Raj advice on relationships.

Amy finds out that Sheldon applied for a one-way mission to colonize Mars; a trip to the pet store leads to a fight; Leonard has a surprise for Penny; Raj is busted while snooping in Emily's apartment.