After discovering a parallel universe hidden inside a supercomputer, four students must stop a renegade virus from destroying the secret world.

The Lyoko Warriors have their work cut out for them as XANA gains power, with an ability to possess humans and create even more mayhem on Earth.

As Season 3 opens, XANA has escaped from the supercomputer and is bent on destroying Lyoko so that the Warriors will be unable to stop his evil plots.

Jeremy and Aelita must rebuild a new Lyoko to replace the one XANA maliciously destroyed at the end of the third season.