The professor is bored being old and decides to switch bodies with his intern, Amy. When they get tired of the game they decide to switch back, only to discover its not possible to swap with the same person twice. Bender agrees to swap between them to get everyone back in order, but only after he commits the perfect crime.
Did You Know?
In 1999 the Stargate SG1 episode 'Holiday' had the same can't-swap-back problem with the same circuitous solution. See more
Amy, inside Leela's body, made Leela obese, but in the closing minutes of the episode, Leela's body is thin again without any explanation. The same for the professor's body, which Amy porked up. See more
Tonight at eleven...
References The Prisoner of Zenda