She tried to pull away, shaking her head.

"Mother," Jas insisted, pulling her closer still, "I'm a Swipe. I got the answers from the teacher's mind."

She shuddered. "Impossible," she said softly.

"I know."

She got up from the table and took him by the hand. Together they left the flat and walked down corridors and ramps to the tube. At that hour it wasn't crowded. She dragged him along until they got to a women's lavatory. She started to pull him in.

"I can't go in there," Jas whispered.

"You're sure as hell going to," she hissed back, her face ugly with fear.

He went in. It was empty. His mother leaned against the door, facing him.

"Maybe," she said, "this place isn't bugged. But if it is, we won't be known."

"Voiceprints."

"Whisper, then," she whispered. "I said it's impossible. I've had two blood tests. Once before your father's trial, and this time for you. I do not have the Swipe on any of my lousy DNA. My X chromosomes are clean. Do you understand that?"

"I know what I did."

"You couldn't have gotten the trait from your father," she said, holding tightly to the boy's arm, "because it's carried on the X and he only gave you a Y."

"I've taken genetics."

"Then why did you say what you did?"

"Separate mutation," Jas said, and she clenched her grip on his arm. It hurt, but he was afraid to try to pull away. He had never seen her this angry and afraid at the same time.

"Do you think they didn't check that? It's the first thing they check. Your cells don't show any mutation."

"Then it's magic," Jas said, and she relaxed just enough that he felt safe in trying to pull his arm free. She let him.