Amy and Sheldon video chat while Amy is away at Princeton. 

Later, when the guys are having lunch at work, Sheldon runs into a former admirer, Ramona, who is now doing research at Cal Tech.

The guys worry about their interaction, noting that she touches Sheldon's hand and he doesn't pull away.

Sheldon tells Amy on video chat later that he had lunch with her, and she wonders if she should be worried.

At the comic book store, Leonard, Raj, and Howard discuss Sheldon's friend, and decide they should get someone to ask her out to find out how she reacts. Of course, Stuart volunteers.

Raj steps up and tries to ask her out, but she turns him down.

Sheldon brings Ramona to meet everyone at the apartment, and everyone tries to keep them separated. Sheldon introduces Ramona and Amy over video chat, and Amy is immediately concerned. 

Finally, Ramona leaves, and Penny has a talk with Sheldon to explain the problem. Unfortunately, Sheldon still doesn't seem to understand, and thinks the whole thing is innocent. 

Ramona brings Sheldon lunch, and when he asks about her motivations, she kisses him.

He immediately gets up, leaves for the airport, flies to New Jersey, and knocks on Amy's door. When she opens it, she sees him down on one knee with a ring.