Shadows in the Frost

Thalia spoke up at once. "Don't turn around. Drive straight through. That roadblock is an illusion. It isn't real."

If they turned the car around now, that would be walking right into the trap.

"An illusion? How is that possible?" Harvey rubbed his eyes hard, but all he could still see was a vicious barricade bristling with spikes.

Magnus immediately said, "Do what Thalia says. Drive through it."