Lois' pregnant sister inspires her and Peter to have another baby.

Peter gets a vasectomy and loses all his sex drive. Lois begins to gain weight, and as a result, Peter's regains his interest in his wife. When Lois' habits get out of control, she has a heart attack. The surgeon must remove Lois' fat to reach her heart, returning her to her normal weight. Meanwhile, Stewie's half-brother Bertram returns to confront him, where they have a war for control over the playground.

Stewie and Brian go back in time to stop Bertram from killing Leonardo da Vinci in order to erase Stewie from the universe.