The Big Bang Theory

The gang deals with the awkward aftermath of an overnight liaison between Sheldon's mother and Leonard's father.

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. Also, Penny and Amy go to a "party" at the house of Bert, the geologist (guest star BRIAN POSEHN). And Raj learns Bernadette's true feelings about her pregnancy when they clean out the future baby room. Dean Norris returns as Air Force Colonel Williams.

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

Leonard and Penny must separate a quarreling Sheldon and Amy, when their cohabitation experiment doesn't go as planned. Sheldon threatens to break off their relationship when Amy refuses to adhere to the "bathroom schedule." Also, Howard and Bernadette find unexpected guests at their house when they decide to stay home from a planned vacation.

Penny is surprised to learn she has fans of her performance in "Serial Ape-ist" when she attends the Van Nuys Comic-Con with Leonard. Also, Amy hosts a Sheldon-style brunch at Penny's apartment. And Howard makes an impulsive purchase when he starts stressing out about the baby on the way.

In order to continue living with Sheldon, Amy lies to him about repairs being made to her apartment; and they host an "on location" episode of "Fun with Flags" in Penny's apartment. Also, Leonard lets Penny decorate Sheldon's old room after he learns that she has secretly been moving Leonard's collectibles into storage.

After a successful experiment combining their genes, Sheldon will stop at nothing to convince Amy they should procreate. Also, Raj is embarrassed to tell the gang what the new woman he's dating does for a living.

When CalTech geologist Bert (recurring guest star BRIAN POSEHN) wins the MacArthur Genius Fellowship, Sheldon is overcome with jealousy. Meanwhile, Howard finds an old remote control Stephen Hawking action figure he invented. STEPHEN HAWKING returns to guest star as himself.

A battle ensues when Leonard and Sheldon argue over who will get custody of their shared belongings. Also, Raj and Stuart fight to be the most helpful during Bernadette's final weeks of pregnancy. CHRISTOPHER LLOYD guest stars as Theodore.

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, Mary.

After Penny feels that Leonard is taking her for granted, she decides to go on a spa weekend with Amy, leaving Sheldon to play the unlikely peacemaker. Meanwhile, Howard and Raj try to fix a squeaky floorboard in the baby's room.

Sheldon beta tests an MIT invention that helps him read people's emotions. Meanwhile, Raj invites his ex-girlfriends over to give him dating advice, and Leonard can't hide his feelings when Penny announces that her brother is coming to town. Guest stars LAURA SPENCER, KATE MICUCCI, ALESSANDRA TORRESANI and KATIE LeCLERC return as Raj's ex-girlfriends.

Leonard and Howard try to distract Sheldon with tickets to a historic railway when he slows the progress of their guidance system. Meanwhile, Penny and Amy take Bernadette out for the night, leaving Raj and Stuart to care for baby Halley. Dean Norris returns as Colonel Williams.

Sheldon and Amy have their first fight since moving in together, after he shares intimate details of their relationship with people at the university. Meanwhile, Raj is shocked by the realities of financial independence when he stops receiving support from his father (guest star BRIAN GEORGE).

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. Also, 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. Also, Bernadette nears the end of her maternity leave and must return to work. JOEL MURRAY guest stars as Doug.

Howard and Bernadette have a hard time leaving Halley in daycare when Bernadette returns to work. Also, Bert introduces the gang to his new girlfriend, Rebecca (guest star APRIL BOWLBY)

Leonard isn't thrilled when Penny considers taking a new job offered by her ex-boyfriend, Zack (guest star BRIAN THOMAS SMITH).

After Leonard, Sheldon and Howard celebrate the completion of their top secret Air Force project, they're met with an unpleasant surprise. Also, Amy is offered a summer position as a visiting researcher.

On the tenth season finale, the gang is concerned when Sheldon's former admirer, Dr. Ramona Nowitzki (returning guest star RIKI LINDHOME) resurfaces while Amy is away at Princeton.