A young Irish teen named Lucas hangs out with a group of punks in an abandoned castle. He appears to be a mutant, and wanders into the depths of the castle dungeon where he has kept a boy named David captive. Lucas encourages David to call for help.
In the middle of the night, Charles Xavier receives a mysterious phone call from someone requesting his help, and claiming to be his son.
The next morning, Xavier sets out in search of this mystery son. Ororo, Scott and Jean accompany him on this trip. On the X-Jet, Xavier is on the phone with his ex-wife. Scott and Jean try to eavesdrop, but Ororo promptly diverts their attention to checking on a sick Kitty in the mansion.
Beast is getting ready the new mutants for school. After receiving Scott and Jean’s message from the X-Jet, he goes to check in on Kurt (who has caught the bug too) and Kitty.
Xavier has been feeling uneasy getting weird looks from Scott and Jean. He finally comes clean with the truth. He was married briefly to a woman named Gabrielle Haller and they had a son he knew nothing about. Now she seeks his help to find her kidnapped son.
Xavier’s relationship with Gabrielle is highly strained. He is furious that she had been keeping his secret from him all these years. She replies that it was for David’s own good; she didn’t want him “growing up with a father who didn’t have time for him”.
David manages to escape from the dungeon, only to be cornered to a cliff. Meanwhile, Lucas makes his way to David’s residence, and catches a glimpse of Jean in the window of David’s room and is intrigued by her.
Scott and Jean are going through David’s belongings to search for clues regarding his disappearance. Jean notices a boy in the doorway and runs after him. He disappears down the hall. Gabrielle tells Scott and Jean that the boy’s name is Ian, and David took him in from the streets. She tells Jean that Ian doesn’t talk, but Jean is determined to probe his mind, telepathically. She runs out the door and is telepathically ambushed by Lucas, who takes her captive.
Meanwhile, back in Bayville, Kitty’s worst nightmare is realised when Kurt teleports them to school in their pajamas while she was tissue-hunting in Kurt’s room.
Storm and Scott go in search of Jean after she went missing. Storm spots fires burning in the castle in the distance. Gabrielle tells them that it’s a popular teenage hangout. Scott insists that he look for Jean there. Xavier and Storm carry on their search for Ian.
At the castle, it is Jean who finds Scott and drags him into hiding.
Jean: “Scott, stay out of sight.”
Scott: “Jean? What happened to you?”
Jean: “David’s here some place.”
Scott: “How did you get here?”
Jean: “I was following Ian. And that”s when Lucas showed up.”
Jean: “Lucas. He’s the one who brought me here. And he took David.”
Scott: (In an angry tone.) “Then it’s time I introduced myself.”
Jean: “No Scott don’t! His powers are too strong!”
Lucas: “Ah, I see the boyfriend has come to crash the party. Up for some fun?”
Scott: “Listen Dracula. Kidnapping two people isn’t my idea of a good time.”
Lucas: “Well then.” (Lucas tosses Scott into a wall telekinetically.) “Is that entertaining enough for you?”
Jean runs to Scott’s aid but is tossed aside by Lucas as well. A fight breaks out. Lucas is mysteriously able to deflect Scott’s optic blasts. Scott is knocked unconscious and tied up to a wall. Lucas puts Jean into the dungeon after Jean tries to put up a fight with her powers.
Xavier, Storm and Gabrielle find Ian on the way to McFadden castle. While trying to telepathically probe Ian’s mind, Xavier finds out he is a mutant, and is working with David’s captive. Ian flees in the direction of the castle and the three chase after him.
Jean finds David in the dungeon and helps him break out. Jean finds out from David that the kidnap was a set up so Lucas could go “brain to brain with the great Charles Xavier”. Jean had to get to Xavier before Lucas did.
Xavier, Storm and Gabrielle find and release Scott, just as Jean and David find their way out of the dungeon. Scott and Jean, and David and Gabrielle savour their reunions for a few moments. Gabrielle introduces David to Xavier. David then reveals his true identity, that he is Ian and Lucas all at once.
Lucas is angry at Xavier for abandoning him and seeks his revenge. David tells Xavier to leave at once, but Xavier insists that he can help. He is drawn into a telepathic battle with Lucas and Ian, but it is a trap set up by Lucas. Having banished Ian and David, Xavier has made Lucas stronger than ever.