Melissa Rauch

Leonard realises that he's the only one of the gang without a girlfriend, while Sheldon wants to get rid of his when she hatches a plan for him to meet her mother.

An embarrassing secret of Wolowitz's comes to light as he tries to win back his ex-girlfriend, Bernadette; Sheldon and Raj have a small war at work.

Tensions run high when Bernadette runs into her hulk of an ex-boyfriend at a science conference. Threatened by Bernadette's ex-boyfriend, Wolowitz has an argument with Bernadette and causes chaos.

Sheldon agrees to take part in a short lecture series at the university, but worries that the students don't seem to like him. On Amy's advice, he asks Penny to give him acting lessons so that he can engage with his audience better.

Bernadette receives her PhD and the gang begin to tease Wolowitz for being the only one among them who isn't a doctor. Meanwhile, Koothrappali becomes Sheldon's new flatmate after hearing Leonard and Priya engaging in a Star Trek bedroom fantasy.

Wolowitz is torn between taking things to the next level with Bernadette and pleasing his mother. Meanwhile, Leonard rekindles his relationship with Raj's sister, Priya.