Family Guy: Season 6, Episode 4

6 - 4: Stewie Kills Lois

In the 100th episode, Lois and Peter go on a cruise, leaving Stewie and the family behind. Upset with Lois for leaving him at home, Stewie vows to carry out a diabolical plan. When Brian challenges him to actually do it, Stewie stows away on the ship, finds Lois and - well - the title of the episode says it all.