Sheldon has been riding the rails across the country and returns a changed man — or at least one who's been robbed. Leonard and Penny pick up the pieces.
Sheldon becomes a junior professor and his teaching style is exactly as difficult as you'd imagine. Howard is his first student.
Howard throws out the first pitch at a baseball game with disastrous results. The guys debate whether sports and science mix.
The guys consider opening a comic book-themed bar. The business plan reveals their different personalities and priorities.
The guys try to focus on work but keep getting distracted by personal problems. The productivity struggle is relatable.
Sheldon and Raj explore a mine together for research. The underground adventure tests their friendship and courage.
A misunderstanding about a gift leads to relationship drama across multiple couples. Communication failures are the theme of the day.
Prom night is recreated for those who missed it the first time around. The second chance at a high school milestone is genuinely sweet.
Sheldon considers getting a nose job — wait, it's a septum issue. Either way, his vanity and his principles collide.
The end of the year brings reflection and Sheldon gives a champagne toast. The moment of sincerity catches everyone off guard.
The gang throws a holiday party with a secret Santa twist. Sheldon's competitive approach to gift-giving creates chaos.
Leonard and Sheldon spend a day doing what the other person wants. The role reversal is eye-opening for both of them.
Leonard's anxiety about his upcoming wedding to Penny creates unusual coping behaviors. The gang tries to help him relax.
Sheldon co-authors a paper and the online comments section becomes a battlefield. Internet trolls meet their match.
The comic book store faces closure and the gang rallies to save it. Stuart's livelihood and their hangout spot are at stake.
An intimacy experiment designed by scientists forces pairs to answer deep questions. The exercise reveals hidden feelings.
Howard and Raj consider starting a Mars colony application. Bernadette is not thrilled about the interplanetary move.
A freezer full of leftovers from Howard's mom becomes emotionally loaded after she starts dating. Howard processes the change.
The guys visit Skywalker Ranch, fulfilling a lifelong dream. The pilgrimage doesn't disappoint.
Sheldon discovers he has a half-brother through his father. The family revelation opens old wounds and new connections.
The gang has to decide who gets credit for a shared discovery. Professional ego meets personal friendship.
Howard is asked to give a commencement speech and his confidence wavers. The gang helps him find his voice.
Sheldon's mom and Leonard's mom meet, and the personality clash is spectacular. Two very different mothering styles collide.
The season finale — Leonard and Penny elope in Las Vegas, but a confession during the drive threatens to unravel everything before it starts.