Sheldon will get a really big surprise when he visits his mom in Houston during Thursday's all-new episode of "The Big Bang Theory."

In the last episode, Howard tried to mend his cantankerous relationship with Sheldon by inviting him on his trip to Houston. During the episode, viewers learned about the origin of their relationship and Sheldon admitted that he is jealous that Howard is an astronaut and he is not.

Meanwhile, Leonard and Penny's relationship took another leap forward when Leonard surprised her with a car to use after her old one broke down. According to CarterMatt, the new car signals that Leonard is trying to be supportive of Penny's career goals so that she can continue pursuing her dream.

The setting in the next installment, "The Mommy Observation," will continue in Texas as Sheldon will discover something new about his mother while he is there.

In the meantime, the rest of the geeky gang will play Raj's Murder Mystery game when Stuart arrives at the apartment and drops dead. The game will also inspire the crew to envision where they think they will be 20 years from now.

CBS Express issued an official synopsis of episode 18: "When Sheldon visits his Mom in Houston, he will be forced to confront a new reality. Meanwhile, Raj's 'Murder Mystery' party will start some fights within the gang."

"The Big Bang Theory" S7E18, "The Mommy Observation," will air on Thursday, March 13 at 8 p.m. EST on CBS.