Penny obtains a new boyfriend that she soon angrily dumps because he blogged details of their sex life. Leonard tries to comfort her and ends up getting her to apologize to the boyfriend. Penny then finds out that he has already found another girl. She responds with anger and sadness towards Leonard, saying that she wants a boyfriend who actually cares about her. Leonard suggests himself. A little surprised, Penny agrees.
Later on, however, they both have doubts about their date, worrying that it could ruin their friendship. Penny asks Sheldon for advice, as she could not ask Raj, Howard, or Leonard. Sheldon suggests to her the theory of Schrödinger's cat, meaning that she'll never know unless she goes out with Leonard. However, Penny does not understand the scientific, literal Schrödinger's cat and so is only confused by Sheldon. At lunch, Leonard also expresses worries to Sheldon. He says to him "Schrödinger's cat" and Leonard instantly understands it.
When Leonard goes to Penny's apartment for their date, there is a somewhat awkward moment before Leonard asks Penny if she has ever heard of Schrödinger's cat. She says she has heard far, far too much about it, to which Leonard responds "Good" and kisses her. Penny finally understands the metaphor, saying the cat's alive and that they should go.
Meanwhile, Sheldon has been learning Mandarin Chinese with the assistance of a reluctant Howard. This is because he wants to express his anger to the owner of a Chinese restraunt which has changed their tangerine chicken to the lesser orange chicken. Leonard and Penny go to this restraunt for their date but see Sheldon yelling severely meaningless Chinese at the restraunt owner. They hurriedly leave.