The White Asparagus Triangulation Sheldon can barely contain his joy when Leonard starts dating a woman who meets Sheldon's exacting standards.
The Vartabedian Conundrum When Leonard's relationship with a new woman starts moving too fast, he goes to Penny for advice.
The Bath Item Gift Hypothesis Christmas is a source of stress for Leonard, whose handsome colleague starts dating Penny, and his friends who are being tormented by Sheldon's obsession with gift-giving etiquette.
The Killer Robot Instability When Penny's comment about Wolowitz's love life sends him into a depressed stupor, his friends lose their most important teammate in an upcoming fighting robot competition.
The Friendship Algorithm Sheldon's intelligence, which renders him socially awkward, is also the source of his new scientific procedure for making friends.
The Financial Permeability Sheldon's "simple" solution to Penny's financial problem leads to a confrontation between Leonard and Penny's hulking ex-boyfriend, Kurt.
The Maternal Capacitance A disastrous visit from Mrs. Hofstadter brings Leonard and Penny closer together.
The Cushion Saturation A paintball game leads to a fight between Penny and Sheldon, and romance for Wolowitz and Leslie.
The Terminator Decoupling A train trip to San Francisco takes a major detour when Leonard, Sheldon, Wolowitz and Raj discover that beautiful sci-fi actress Summer Glau is onboard.
The Work Song Nanocluster Penny's home hair products business becomes a complete nightmare when a caffeine-addled Sheldon takes over.
The Dead Hooker Juxtaposition Penny develops a rivalry with a sexy female neighbor who threatens to become "The New Penny" in the building.
The Hofstadter Isotope While a fellow comic book-loving pal of the guys romances Penny, Leonard and Wolowitz venture out into the world of "Ladies' Night" at a local bar.
The Vegas Renormalization Leonard and Koothrappali take a heartbroken Wolowitz to Las Vegas, leaving Sheldon locked out of his apartment and forced to bunk with Penny.
The Classified Materials Turbulence Things begin to look up for Leonard when Penny makes a surprising revelation on her second date with Stuart. Meanwhile, Wolowitz enlists his friends' help when he discovers a critical design flaw in his project for NASA.
The Monopolar Expedition Penny is conflicted when Leonard and his friends decide to spend the summer working - at the North Pole.