In 1945 Las Vegas, World War II veteran Frank Harris (Brad Pitt) returns to his mother. Riding on a motorcycle that he won in Italy during his service, Frank and his mother are struck by a drunk couple. Frank survives, but his mother dies. As an ambulance takes her away, Frank is transported to "Cool World", an animated city of surrealistic landscapes and random cartoon violence. He was inadvertently teleported by Dr. Vincent Whiskers (Maurice LaMarche), a doctor who created a "spike" that was supposed to take him to the real world, but brought Frank to Cool World instead. Whiskers finds Frank useful enough to run things in the Cool World while he is gone to the real world.Forty seven years later, Jack Deebs (Gabriel Byrne), a cartoonist, is detained after murdering a man he found in bed with his wife. He creates the highly acclaimed comic book series Cool World, which features the femme fatale Holli Would (Kim Basinger). On the night before his release, Holli summons Jack into the Cool World, and he sees Holli dance in the local dance club. After he sees her dance, Jack is teleported back to the real world. It turns out that Holli wants to enter the real world, but is forbidden to do so by Frank, who is now a detective for the Cool World Police Department.After he is released, Jack is transported to the Cool World once again and meets Holli and her goons Slash (Joey Camen), Mash (voiced by Maurice LaMarche), Bash (Gregory Snegoff), and Bob (Candi Milo). They have been encouraging his misled beliefs that he himself created the Cool World. In reality, Holli has simply been bringing him there, and Jack created his comic book series on what he's seen there, which he initially believed were his own dreams. Meanwhile, Frank is about to go on a date with his longtime girlfriend Lonette (Candi Milo) when his partner Nails the Spider (Charlie Adler) tells him about Jack's presence. Holli and the Goons take Jack to the local Slash Club where Mash uses his motives persuade the bouncer Chico (Patrick Pinney) to let Jack into the club. While in the club, Jack is then confronted by Frank who puts him against the wall as Jack claims he has no knowledge of "drawing" Frank. While confiscating his fountain pen and stating that he is with the Cool World Police Department, Frank informs Jack that his fountain pen is a dangerous weapon in the Cool World. Frank then tells Jack the truth: Cool World has existed long before he created the comic series and forewarns him that "noids", real humans from the real world, are not allowed to have sex with "doodles", the cartoon inhabitants of the Cool World. He further advises Jack not to get involved with Holli before Jack returns to the real world.Holli brings Jack back into the Cool World, where he is taken to Holli's apartment. Holli and Jack have sex, transforming Holli into a real human. While Frank attempts to mend his relationship with Lonette, he temporarily leaves detective duties to Nails. Nails receives a call from an informant named Sparks, who tells him that Jack and Holli have had sex and are leaving for the real world. Nails decides that he can do this on his own and goes off to stop Holli. Nails attempts to stop her from leaving the Cool World, but Holli uses Jack's fountain pen to suck Nails in. Jack and Holli return to the real world, where Holli sings "Let's Make Love" at a nightclub with Frank Sinatra, Jr.. Frank discovers that Nails is gone and decides to venture into the real world to pursue Jack and Holli. Meanwhile, Jack and Holli have started to flicker between real and doodle states. While contemplating their situation, Holli tells Jack about the "Spike of Power", an artifact placed on the top of the Union Plaza Hotel by a doodle who crossed into the real world. When Jack displays skepticism about Holli and the idea, Holli abandons him to search for the spike on her own.Frank meets up with Jack later on, explaining that the flickering both Jack and Holli have been experiencing is the disappearance of both worlds. They decide to team up and stop Holli from removing the spike. They get Jennifer (Michele Abrams), the daughter of Jack's neighbor to drive them to the casino. In the way, Frank explains that it was Doc Whiskers who crossed worlds and put the spike on the top of the hotel and if it were removed, it could potentially destroy both the real world and the Cool World.Holli is escorted out of the casino for not spending any money, all the while asking about Vegas Vinnie, which is the alias of Doc Whiskers. When she spots the Doc, she tells him that she couldn't find him. When she starts to flicker between real human and doodle state again, she begins to become suspicious and starts to see through Doc's disguise and shakes him out of it, revealing his identity. Doc tries to convince Holli not to get the Spike of Power, but Holli becomes enraged and threatens Doc Whiskers with the fountain pen. When Frank, Jack, and Jennifer get to the destination, Frank pursues Holli on the casino, while Jack and Jennifer put Doc Whiskers back together after being popped by Holli's pen. Frank chases after Holli throughout the hotel, while she's still flickering from real to doodle state. While in doodle form, Holli pushes Frank off the building to his death.Holli finds and takes the Spike of Power, transforming her, Jack, and everyone in Vegas into doodles and opening a gateway between the two worlds, releasing numerous monstrous doodles. When Jack is transformed into a superhero doodle called Super Jack (Maurice LaMarche), he gets a hold of the spike. Holli tries to seduce it away from Super Jack. Instead, he returns the Spike of Power to its place trapping him, Holli, and the rest of the doodles in Cool World.Meanwhile, Nails escapes from Holli's pen as he and Doc Whiskers return Frank's body to Cool World. Lonette discovers that Holli was a doodle when she killed Frank. She explains when a noid is killed by a doodle, he is reborn in Cool World as a doodle. Frank is then revived as a doodle, allowing him to pursue his relationship with Lonette. Meanwhile, Super Jack and Holli are last seen together in the panels of a comic book. Super Jack is planning out how they will live, much to Holli's dismay.
Output: Question: What keeps the Interworld Matrix intact?, Answer: Spike of Power