The Simpsons go on a trip to the Springfield beachfront area. Whilst at the beach,
Bart becomes angry over
Lisa's good fortune when she becomes happy with a new sunhat she finds, while he becomes sad over the failure of his "Bad to the Bone" temporary tattoo because it is not waterproof. On their way home, Bart takes her hat while she sleeps in the car and tosses it out the window into a junkyard. When Lisa finds out that it is gone, she becomes inconsolable, leading Bart to receive the first visit from his "guilt monster", a slime-covered creature that reminds him of what he did, that grows and becomes progressively hideous the more Bart denies his guilt. After enough visits, Bart accepts his guilt and tells Lisa the truth, but she feels wounded by his actions and refuses his attempts to make amends with her. To redeem himself, Bart returns to the junkyard to recover the hat, only to discovers that it has become a part of a car that had been crushed into a cube, so he breaks the hat free from the car. However, when he gives the hat to Lisa, she bluntly rejects his apology and tells him to focus on being a brother to
Maggie. Suddenly, Lisa has a vision of her own emotional spirit, who says that her brother was trying to make amends, so she forgives Bart. Meanwhile, after being forced by
Marge to do something other than leer at women beach volleyball players,
Homer plays chess and finds he is of grandmaster strength, much to the shock of himself and everyone else. As Homer plays more chess, he realizes he used to play the game with
Grampa as a way of bonding with him after his mother
Mona left, but often lost to his father until he was given lessons in chess by a professor who lived nearby. After improving his game and finally beating Grampa, his father angrily refused to play against him anymore. Homer thinks his restored ability is an indication he secretly wants to kill Grampa. Taking advice from chess champion
Magnus Carlsen, Homer encourages his father to play again with him. Homer allows him to win, in hopes of closing the wound from their past. ==Production==