After Sheldon's mother and Leonard's father share an evening together, everyone deals with an awkward "morning after the night before" in the tenth season premiere.

Colonel Williams, an Air Force representative from the Department of Material Command, sits down for a talk with Howard.

Tensions rise when the guys struggle to complete their government project on time - and Sheldon tries an energy drink to stay awake. Meanwhile, Penny and Amy go to a geologist's "party".

When Amy's apartment floods, she proposes a "cohabitation experiment" with Sheldon. Meanwhile, Raj learns the gender of Howard and Bernadette's baby….before they do.

Sheldon threatens to break off their relationship when Amy refuses to adhere to his "bathroom schedule", putting their cohabitation experiment in jeopardy.

Penny learns there are fans of her performance in "Serial Ape-ist" when she and Leonard attend a Comic Con event; Amy hosts a brunch at Penny's apartment; and Wolowitz makes an impulsive purchase.

Amy lies about repairs being made to her apartment so she can continue living with Sheldon; Leonard lets Penny decorate Sheldon's old room.

After a successful experiment combining their genes, Sheldon is determined to procreate with Amy. Meanwhile, Raj is embarrassed with his new date's occupation.

Sheldon struggles to contain his jealousy when CalTech geologist Bert wins the MacArthur Genius Fellowship. Stephen Hawking returns for a guest appearance.

A battle ensues when Leonard and Sheldon argue over who will get custody of their shared belongings. Christopher Lloyd guest stars.

While Sheldon and Amy celebrate Amy's birthday, Howard and Bernadette welcome their new Baby Wolowitz.

Sheldon and Amy visit Leonard and Penny for the first time since the holidays and share details about their terrible trip to Texas. Laurie Metcalf returns as Sheldon's mother.

When Leonard and Penny fight, Sheldon plays the unlikely peacemaker. Meanwhile, Howard and Raj try to fix a squeaky floorboard in the baby's room

While Raj gets dating advice from his ex-girlfriends, Sheldon gets help reading people's feelings when he beta tests an emotion-detection invention.

Leonard and Howard try to distract Sheldon by giving him tickets to a historic railway, while Penny and Amy take Bernadette out for the night, leaving Raj and Stuart with the baby.

Amy is furious when she learns Sheldon has shared intimate details of their relationship with people at the university, prompting their first fight since moving in together.

When Raj is cut off from his father's fortune, he appoints Sheldon in charge of his finances to help him get out of debt. Meanwhile, Penny considers joining Leonard at Comic-Con.

When Raj moves out of his apartment, Leonard and Penny offer him Sheldon's old room. Christine Baranski returns as Leonard's mother, Beverly.

Leonard, Penny and Raj adjust to their new living arrangement, while Sheldon takes an interest in Amy's work.

Sheldon pushes himself to the limit when he collaborates on projects with Leonard and Howard as well as Amy on the same day. Meanwhile, Bernadette nears the end of her maternity leave.

Howard and Bernadette have a hard time leaving Halley in daycare when Bernadette returns to work. Meanwhile, Bert introduces the gang to his new girlfriend, Rebecca.

Leonard isn't thrilled when Penny considers taking a new job offered by her ex-boyfriend, Zack.

After Leonard, Sheldon and Howard celebrate the completion of their top secret Air Force project, they're met with an unpleasant surprise.

On the tenth season finale, the gang is concerned when Sheldon's former admirer, Dr. Ramona Nowitzki resurfaces while Amy is away at Princeton.