David Haller, Xavier's son, who has lived away from his father's knowledge, contacts him seeking help. He has been kidnapped by a man called Lucas.
Xavier, Jean, Scott and Storm travel to Scotland where Xavier's ex-wife lives with David and a street boy called Ian. When Ian leaves the house, Jean follows him and is kidnapped by Lucas. Scott tracks them to an old castle in ruins where teenagers throw parties and gets captured. Xavier and David's mother find Ian and with his help, they get to the castle and face the boys there while Jean, Scott and David escape. David meets his father for the first time, and he reveals he is actually Ian. Lucas, too, by turning into Ian first and later into Lucas. His multiple personalities change his appearence every time. Xavier enters in his son's mind trying to erase Ian and Lucas, but fails and Lucas is the only one left who disappears in the sky.
Meanwhile, at Bayville, Kitty and Kurt are way too sick to go to school.
Loosely following the main stories from the original comic, X-Men: Evolution accompanies the lives of six mutants (Cyclops, Jean Grey, Nightcrawler, Shadowcat, Rogue, and a new original character named Spyke) who attend Xavier's Institute for the Gifted, where they ought to learn how to control their powers and use them for good.
These teenagers must face a world that both fears and despises them.
X-Men: Evolution - Sins of the Son Synopsis and Schedule