Ep 20. The Hofstadter Isotope

Leonard and Penny are officially dating again and Sheldon has to cope up with it as he is not accustomed to change. Meanwhile, Leonard's world is shaken up by a young woman named Alicia who asks him out on a day. They met in the comic book store while buying The Green Lantern comics, and since then Alicia has been on Leonard's mind. The guys bring up the 'assertion' theory that if a man does not ask a woman out who has shown interest, then he is implying he's not interested. Leonard, not wanting to be unfair or lead Alicia on, decides to go on a date with her.

After the date, Leonard finds out from Alicia that he was the first physicist she had ever been out with - and he is honored. The guys make fun of him for being happy that he was Alicia’s first physicist. Over dinner, Leonard tells the gang a story about how he got drunk and kissed a girl at a party who turned out to be his cousin. Sheldon, uncannily remarks that he had predicted that this would happen. Leonard is embarrassed and tells the crew to keep this quiet, but Howard cannot help but announce it to everyone at the comic book store.

Penny starts feeling insecure about her intelligence and convinces herself that Leonard wants a smarter girlfriend since his date, Alicia, is more intelligent than her. She decides it's time she gets a college degree, but doesn't get off to a good start with her history lecturer who did not want to hear about Tomb Raider. Despite this, she attends class the next day only to discover that Sheldon is there too as he won't let her out of sight. Sheldon starts answering all the questions and the professor thinks he is smarter than Penny.

Howard meets his soul mate, a woman named Bernadette, who is not only good-looking but also has a great understanding of many things that Howard likes, such as telescopes, robot arms, and ant farms. They share a kiss and Howard thinks he has found true love. Everyone doubts her existence and Howard is convinced that she is the one, until they see her interacting with Howard at Pasadena City Hall.