After being invited to Switzerland to see the CERN Supercollider (the world's largest and highest-energy partile accelerator), Leonard wants Penny to join him on the travel, making it a romantic Valentine's Day getaway. Sheldon becomes shocked that he can't go when he has a far bigger interest in the science, and tries to change Leonard's mind in all sorts of ways. Meanwhile, Leonard fears that no matter which of them he'll pick, the other will be angry and he will lose a friendship... or a relationship.