The Spoiler Alert Segmentation
Leonard is reading Harry Potter and the Half Blood Prince but Sheldon spoils the ending. After a heated argument, Leonard leaves their apartment and moves in with Penny. She is uncomfortable with this but cannot persuade him to move back. Amy, discovering Leonard has moved out, wants to move in with Sheldon, making him uncomfortable. Later, Penny and Sheldon comfort each other over their similar predicaments and decide to tell their partners the truth. When Sheldon tells Amy to leave she is incensed. He is scared and says Leonard might return since Penny does not want him living with her. A brief spat between the four ensues. A dejected Leonard moves back to Sheldon, who thereupon spoils the plot of a The Walking Dead episode. Amy, angry at the men, considers moving in with Penny, making her uncomfortable again. Meanwhile Howard, joining Bernadette and her colleagues on a Las Vegas trip, asks Raj to check on his mother, depressed since splitting with her dentist boyfriend. Raj, noting her depression, stays the night. She pampers him just as she did Howard, and hides his clothes and car keys to prevent him leaving. When he tries to escape from Howard’s bedroom window, she pulls him back in.
Title reference: After Sheldon spoils the ending of Harry Potter and the Half-Blood Prince, Leonard elects to move in with Penny. The concept of spoilers is used a few times throughout this episode.