"The Bob Next Door" is the twenty-second and penultimate episode of the twenty-first season of the American animated television series The Simpsons.

Eventually, Bart discovers that Bob has surgically swapped faces with Walt, who was his cellmate at that time, and still plans to kill him, although he is ultimately defeated.

Marge convinces him otherwise by taking him to the penitentiary, where they see Bob locked in a padded cell, wearing a straitjacket and writing "Bart Simpson Will Die!"

A seemingly reassured Bart decides to go to a baseball game with Walt, who removes his small shoes to show long feet folded inside, revealing himself to be Sideshow Bob.

Bob restrains Bart in the car and gags him with duct tape, planning to take him to Five Corners, a location where five states meet, to kill him.

Meanwhile, the real Walt Warren escapes prison while bearing Bob's hair and face and comes to the Simpsons' home.

Amidst a distraction outside the diner, Homer, Marge, and Lisa travel to Mexico in search of Bart while Walt gets away and continues to the Five Corners.

[2] Bart tries to tempt Walt to sing "Three Little Maids From School Are We" from The Mikado; the same song was also used in an earlier episode, "Cape Feare", which also featured Sideshow Bob.

Later in the show, when Sideshow Bob reveals his true identity, he exclaims he is now "able to sing all the Gilbert & Sullivan I damn well please", followed by him pulling a Japanese fan out of the glove box and singing the opening notes of "Behold The Lord High Executioner", another number from The Mikado, to Bart's horror.

[2] In its original American broadcast on the Fox network on May 16, 2010, "The Bob Next Door" was viewed by an estimated 6.258 million households and got a 2.9 rating/9 share in the 18–49 demographic.

It came second in its time slot after the season finale of Survivor: Heroes vs. Villains and became the second highest-rated show in Fox's "Animation Domination" programming block after a new episode of Family Guy, according to the Nielsen Media Research.