Tim Allen, Sigourney Weaver and Alan Rickman star in this post-modern sci-fi comedy.
The three actors play the has-been stars of a long since-cancelled Star Trek-esque show called Galaxy Quest who now earn a meagre living appearing sci-fi conventions, mall openings and the like.
But one day they (and the rest of the cast of the Galaxy Quest cast, including Tony Shalhoub [Monk] and Daryl Mitchell) are abducted by a race of aliens called the Thermians who have been watching reruns of their show, believing it to be "historical documents". They revere the actors as heroes and are now relying upon them to save their race from extermination.
Also along for the ride is Guy Fleegman (a scene-stealing Sam Rockwell - Confessions of a Dangerous Mind), an actor who once had a bit part on the show.
Now commanding a real-life replica of the spaceship from their series, these actors must take on all manner of intergalactic nastiness for real.
Galaxy Quest derives much of its humour from the various books published by Star Trek cast members in which they detailed their loathing for lead actor William Shatner, the behind the scenes sexual shenanigans and their disappointment at being pigeonholed in their careers. It also pokes considerable fun at the ripe-for-comedy fanbase shows like this inspire
Allen's Jason Nesmith is clearly the Shatner proxy, while Rickman's Alexander Dane takes his cues from Leonard Nimoy's jealousy and the Shakespearean pedigree of Patrick Stewart from Star Trek: The Next Generation.
There are also many in jokes for bonafide sci-fi fans, such as the fact that the Thermians are from the "Klaatu Nebula" - Klaatu being the alien from The Day The Earth Stood Still.
Star Trek: The Next Generation star Jonathan Frakes has referred to the film as an accurate portrayal of what it was like to work on such a show.