Gone Boy

"Gone Boy" is the 9th episode of season 29. It aired on December 10, 2017.

Plot
Sideshow Bob and are collecting trash for community service with other men, but when they finishes the work, the Simpson family runs over it with a rental car. After finishing up the rental time and fuel, Homer goes with Bart to play, but Bart needs to pee and goes in the forest, falling down a manhole.

The family and cops start searching the forest, but the cops fail as usual. Bart finds himself in some kind of bunker, where he finds electronic equipment, which appears to be a military installment. People start looking for him, including Sideshow Bob, Shaquielle O'Neal and the other detenees.

Bart tries to escape, but the ladder gives up, he finds a phone but instead of calling for help he calls Moe for a prank. Milhouse finds the entrance, but fails to help him. The news gives up hope saying he's dead, but Milhouse fails to bring the good news, in favour of Lisa's affection.

Sideshow Bob is having issues accepting it, and Bart phones Marge confirming he's alive. When Milhouse leaves the house, Bob appears, convincing him to bring him to Bart, with the family right behind. Bob shoves Milhouse down the manhole and then following immediately. Homer and Grampa fail to find them once again, while Bob ties them up to a missile and tries to launch them and kill both, but he's having regrets, and saves them.

Several years later, an elder Sideshow Bob is seen retired to a lighthouse to still go crazy over killing Bart, even after saving him, writing his message on the sand, just to be washed away by the water. He's heard by Jeremy Freedman, working as a mailman, delivers his mail. Jeremy tells him he wouldn't disturb him for the mail and hear his rant if he gets a mailbox. Bob considers the option for good measure.