At a Simpson-Van Houten family picnic, Kirk and Luann announce that they are re-marrying. They leave Milhouse with the Simpsons while they are away on their honeymoon cruise, but as Kirk tries to carry Luann over the threshold into their cabin, the ship lurches to one side and they fall overboard. Milhouse's faint hope that they are still alive quickly fades, and he decides that with no parents, he has to grow up fast. He soon becomes an emotionally numb loner who earns the sympathy of the other boys (even Nelson) and the adoration of the girls (especially Lisa).
Frustrated at no longer being the coolest kid at school, Bart decides to restore Milhouse to happiness by tracking down his Danish uncle Norbert "Zack" Van Houten in Solvang, California. Zack turns out to be a dashing aviator/adventurer, and Milhouse finally breaks out of his grief-induced shutdown upon their reunion; however, far from restoring Bart's status as the coolest kid in school, the sight of Milhouse's reunion with his Cool Uncle just makes him more popular. Lisa deduces the real reason Bart is upset over Milhouse's popularity: he loves him, and is afraid of losing him as a best friend. When Zack announces that he is taking Milhouse back to Solvang by hot air balloon, Bart grabs onto the rope of the departing balloon and joins them on their adventure. However, they fly toward a desert island on which Kirk and Luann were marooned after falling overboard and which they are now trying to leave by improvised hang glider; the two flying objects collide, re-uniting Milhouse with his parents (and sparking a fistfight between Zack and the ethnically Dutch Kirk).
In a subplot, Marge is unamused to discover that Homer doesn't know the colour of her eyes, and refuses to let him see them again until he remembers. Abe finally points out that Homer wrote a song about Marge when they were first dating, but while he remembers the first verse and a half, he blanks when he gets to the crucial line, knowing only that her eye colour rhymes with "appraisal". Fortunately, Marge hears Homer's performance, and is so touched that she lets him see her eye colour: hazel.
- All Girls Want Bad Boys: When Milhouse becomes a leather jacket-wearing, emotionless loner in response to his parents being lost at sea, all of the girls at Springfield Elementary - especially Lisa - begin swooning over him.
- Bee Afraid: While trying to protect Maggie from a bee, Homer gets his head stuck into a beehive.
- Cool Uncle: Far from the nerd Bart was expecting with a name like Norbert, Milhouse's uncle is a heroic aviator who flies to Springfield in his own biplane, and leaves with Milhouse (and Bart) in a hot air balloon in the episode's final act.
- Emo: Milhouse turns emo to deal with his mourning over his parents.
- Forgotten Anniversary: Homer tries to look at wedding photos to find out the color of Marge's eyes but the album is locked and the passcode is their anniversary, which he doesn't remember.
- Informed Attribute: Apparently, Marge has an eye color (of course, given the fact that the Simpsons characters usually have round eyes with black pupils, Marge's reason for hiding her eyes from Homer and making him feel guilty is irrelevant at best).
- Instantly Proven Wrong: When Milhouse feels his parents are dead, Marge tries to cheer him up by saying there's always hope, only for a Festival Cruise officer to appear at the window to say they have called off the search, much to Marge's ire.
- Kick Them While They're Down: Bart comes up and sprays Milhouse with the garden hose just after he finds out his parents might be dead. The Festival Cruise representatives gesture to him about the bad timing.
- No Sympathy: Homer gets his head stuck into a beehive, falls into a blueberry bush, turning the beehive blue, falls into a green picnic blanket getting wrapped like a dress and the only reaction he gets is Marge berating him for impersonating her.
- Not Helping Your Case: Homer tries to take Milhouse's mind off of his parents being lost at sea, only for everything he keeps offering him to be related to the sea.
- Not Quite Dead: Milhouse's parents fall overboard on their honeymoon cruise, but in the episode's final scene, they are revealed to have made it to a deserted island, which they are about to leave via hang glider when Zack's balloon shows up.
- Product Placement: Of a very specific sort. When Homer tries to cheer Milhouse up the morning after he is told his parents have been lost at sea, he offers him a glass of Ocean Spray cranberry juice. Realising his gaffe, he tries offering him Cap'n Crunch cereal, and proceeds to dig himself deeper with Seven Seas salad dressing, Chicken of the Sea tuna, and CDs of Billy Ocean and the history of Atlantic Records.
- Tempting Fate: When Milhouse is staying with the Simpsons and having fun, he casually says he doesn't care if his parents ever come back. Then two Festival Cruise men show up to tell him the bad news. Naturally, Milhouse blames himself for this.