Jennifer Jason Leigh stars as a computer programmer who creates a virtual-reality game that taps into the players' minds.
Allegra Geller (Jennfier Jason Leigh) is the leading computer game designer in the world. She is currently testing her new virtual reality game, which she has named eXistenZ, on a focus group.
As the group begin their trial, Allegra is attacked by an assassin who is using a bizarre organic gun. She flees with a young marketing trainee, Ted Pikul (Jude Law), who is then assigned as her bodyguard.
Unfortunately, her pod, an organic gaming device that contains the only copy of the eXistenZ game program, is damaged.
To inspect it, she talks Ted into accepting a gameport (an organic 'plug' situated in the gamers' spine) in his own body so he can play the game with her.
The events leading up to this, and the resulting game lead the pair on a very bizarre adventure where reality and their actions are impossible to determine from either their own or the game's perspective.