Liquid Diamond is Forever is Part 2 of the Futurama Simpsons Infinitely Secret Crossover Crisis.
Bender is thrown out of Moe's for doing something with the love testing machine, so Homer gets Ned Flanders to give Bender a room. He later escapes after Flanders catches him doing something else with his jukebox. At the Springfield Retirement Castle, Professor Frink overhears Farnsworth talking with Abraham Simpson and realises that Farnsworth is a genius, and breaks Farnsworth out. And at the Springfield Country Club, Zoidberg "saves" Mr. Burns from choking by using a toaster. Burns makes Zoidberg his personal physician.
Next morning, when school starts, Fry manages to convince Bart that he's telling the truth by showing him the comic they're both in. They fly through Springfield on hovering skateboards using some anti-gravity gum. At the power plant, Zoidberg sneezes over Hermes which causes him to regain his memory. Their talk about the future is overheard by Mr Burns, who kidnaps them.
Lisa takes Leela back to her house, where she complains that Bart gets all the attention. Leela tells her she's a special girl and should take attention if not given it. Maggie enters, followed by Nibbler and Marge - seeing Nibbler gives Leela her memory back. Nibbler quickly fills everyone in on the plot using his mental powers. Fry and Bart arrive, followed by Homer and Bender. Nibbler senses great danger, so everyone gets in the Simpsons' car to head to the power plant. They use the anti-gravity gum to beat a traffic jam, but Homer spits it out after the flavour goes. The car lands on a Duff blimp, but Bender's cigar causes it to explode. Falling again, they are caught by Frink and Farnsworth on their flying motorcycle. Since the car is overweight, Fry (with his holophoner) and Lisa are left behind.
The others arrive at the power plant to find out that Mr. Burns will turn Zoidberg into radioactive bisque unless they take him to their "future world". Farnsworth and Frink have invented a device that might get the Planet Express crew back to their own world, which Burns takes. Smithers then takes it from Burns, and reveals himself to really be Amy in disguise! Unfortunately, the real Smithers, dressed up as Mr. Burns, retakes the device. Just as the real Burns is about to use the device, aliens from the "Galactic Time Council" (who look remarkably like Kang and Kodos, but aren't), arrive with weapons. Burns and Smithers run off, after which it is revealed the aliens are in fact the result of Lisa playing on the holophoner, with Fry doing the voices.
The Professors use their machine, which causes a tear in the comic. Nerdanus XII zaps the brains from the tear, which shatters the barrier around the comic. This means the crew can finally go home..... where it is revealed that New New York is now filled with the citizens of Springfield in an "ironic twist ending".