Galaxy Quest
In the film's universe, the TV series Galaxy Quest was a highly popular space-drama, until it was canceled after only four seasons. Seventeen years after the series ended, the stars of the show have been reduced to convention appearances and store openings. Only Jason Nesmith (Tim Allen), the egomaniacal star and crew "commander", enjoys the devoted fanbase. His other crew members are less enthusiastic, fed up with being typecast by their roles on the show. At a convention, Jason meets an eccentric group of people claiming to be extraterrestrial beings called "Thermians" led by "Mathesar" (Enrico Colantoni), who ask him to appear in what he assumes to be an amateur episode. Jason humors them, whereupon the Thermians transport him to their spaceship to negotiate with Sarris (Robin Sachs), a reptilian humanoid warlord engaged in a genocidal war against them. Sarris demands the "Omega 13”, a device mentioned (but not used) in Galaxy Quest's final episode. Jason thinks the situation is fictional and orders them to attack Sarris before asking permission to return home. Jason is sent to Earth through space in a gelatinous "pod", and realizes the ordeal was real. Jason tells his co-stars about it, and they reluctantly join him and return to help the Thermians.
The Thermians turn out to be a peaceful, naïve, octopoid alien race whose society had fallen into disarray some time ago. However, they then discovered Earth's TV transmissions and, having no concept of fiction, theatre, or lying, mistake the Galaxy Quest episodes as factual "historical documents". Observing the success of the crew in the show, they then proceed to model their entire society after the show's example, building an actual version of the show's spaceship (the NSEA Protector), using "appearance generators" to make themselves appear humanoid, inventing actual versions of the fictional technologies portrayed in the show, and following the show's inspiring ideology. Thus, the human cast is obliged to assume their television roles in order to survive. Sarris attacks the Protector, and the ensuing fight forces them to flee through a minefield, which damages the ship's reactor powered by a "beryllium sphere". The actors travel to a nearby planet to secure a new sphere, and the crew narrowly escapes being attacked by goblin-like natives, leaving Jason behind at the mercy of a giant rock monster called "Gorignak". He is teleported back aboard the ship by Fred (Tony Shalhoub), but in his absence Sarris has invaded and taken control.
Interrogated by Sarris about the Omega 13, Jason reveals the truth about the "historical documents" to him; Sarris understands the truth of the show and orders Jason to tell Mathesar, who is crushed after learning that Jason and his crew are frauds. Sarris returns to his ship while his men remain behind and activate the self-destruct sequence. Using a gambit from the show, the actors escape and proceed to try and rescue the Thermians. To deactivate the self-destruct sequence, which Jason and Gwen (Sigourney Weaver) don't know how to do, Jason contacts Brandon (Justin Long), a Galaxy Quest fanboy with whom he accidentally traded communicators at a convention previously. Brandon, excited at the show being "real" as he secretly suspected, guides Jason and Gwen through the Protector's unnecessarily dangerous inner systems to the core's control center and tell them how to shut down the self-destruct sequence. On the way, Jason and Gwen end up underneath the Omega 13 itself: Brandon reveals that according to fan speculation, the Omega 13 may either be a bomb capable of destroying the universe, or a device which re-arranges all matter in the universe to the state that it was 13 seconds before the device was activated, effectively acting as a time-machine which can send the user back thirteen seconds. Meanwhile, actor Sir Alexander Dane (Alan Rickman) and a young Thermian named Quellek (Patrick Breen) free the Thermian prisoners, and Fred transports the monster Gorignak onto the ship to attack Sarris' soldiers. Taking back control of the ship, the actors and Thermians engage Sarris' ship in combat and destroy it with mines from the aforementioned minefield, child-pilot Tommy (Daryl Mitchell) having practiced piloting by re-watching old episodes of the show. Celebrating their victory, the actors return to Earth.
On the way, Sarris sneaks aboard the ship disguised as Fred and attacks, wounding the crew as the ship nears Earth. Jason activates the Omega 13 and is sent back in time thirteen seconds, long enough to incapacitate Sarris and land the ship in some degree of safety. With Brandon's help to provide a bearing, the crew lift off from the Protector in a separate shuttle craft, leaving the Thermians to pilot the bulk of the ship back to their galaxy. The shuttle crashes at a Galaxy Quest convention, where the crowds assume it to be part of the show. As the crew emerges from the wreck, Sarris revives and attacks, but Jason finally dispatches him with a blaster pistol. This spectacular display leads to a revival of the Galaxy Quest series, starring all the original cast, in addition to a Thermian named Laliari (Missi Pyle), who chooses to stay as Fred's lover, and former redshirt Guy (Sam Rockwell) as a new crew member, "Security Chief 'Roc' Ingersoll".
