They thought Xana was defeated. They were wrong. Xana's alive, but he's weakened. They thought they were safe. They are never safe. The Masters have awakened. Nobody is safe.
There's a lot that happens. First, someone gets blasted back in time. Then that someone learns more about Lyoko and becomes dedicated to stopping XANA. And then there's the supercomputer nearly blowing up and then Ulrich and Yumi got...Okay, let's just start here. One day, Sissi snuck into the factory. Reviewing helps me write better.