Penny, Bernadette, and Amy are out for a much needed girl's night when Penny runs into her ex-boyfriend, Zack. Zack invites Penny and Leonard to have dinner with him and his fiancee.

Meanwhile, Sheldon, Leonard, Howard, and Raj hang out at the comic book store, where Sheldon talks about how he wants to push his brain out of its comfort zone. It's called "super-aging."

Leonard and Penny head to dinner, and Zack is there without his fiancee.

Raj helps Sheldon to learn to make croissants, and Sheldon does great at that too. 

At dinner, Zack offers Penny a job in sales. Leonard doesn't think it's a good idea, and has a problem with Penny wanting to take the job.

Sheldon tries juggling and unicycling, but quits both. Amy points out that he often quits things when he's not good at them.

Leonard and Penny talk about their disagreement, and Leonard says he'll deal with it if Penny wants to take the job. 

Amy tries to make Sheldon feel better when he worries he's going to too old soon to win a Nobel prize. He responds by saying he's going to learn to talk on stilts. 

Penny calls Zack to say she'll take the job, but he says his fiancee thought it was a bad idea.