The Maternal Capacitance
Leonard and Penny are drawn together after a disastrous visit from Leonard's mother.
The Financial Permeability
Sheldon's solution to Penny's financial difficulty leads to a confrontation between Leonard and Penny's ex-boyfriend.
The Friendship Algorithm
Sheldon creates a scientific procedure for making friends.
The Killer Robot Instability
Penny's criticism of Wolowitz's romantic life pushes him into depression and AWOL for a fighting robot battle the rest of guys are depending on him for.
The Bath Item Gift Hypothesis
Penny starts dating Leonard's handsome colleague; Leonard and his friends are tortured by Sheldon's obsession with gift-giving etiquette.
The Vartabedian Conundrum
Leonard asks Penny for advice when his new relationship starts moving too fast.
The White Asparagus Triangulation
Sheldon is thrilled when Leonard starts dating a woman who meets Sheldon's stringent standards.
The Monopolar Expedition
The guys' plan to work over the summer at the North Pole makes Penny revaluate her feelings for Leonard.
The Classified Materials Turbulence
Penny's second date with Stuart sees her making a comment that gives Leonard new hope for a relationship with her. Wolowitz realizes there's a crucial error in a NASA project he's working on.
The Vegas Renormalization
Leonard and Koothrappali escort a heartbroken Wolowitz to Las Vegas, and Sheldon becomes locked out of his apartment and must stay with Penny.