Traveling in a motor home, Adrian Monk is determined to show his agoraphobic brother Ambrose the outside world. But as little crimes pop up along the highway, Monk can't resist getting involved. Now it's up to Monk to stop a murderer from turning their road trip into a highway to hell.
Adrian Monk is feeling strangely satisfied these days-and he'd like his agoraphobic brother to feel the same way. So he takes Ambrose, against his will, on the open road in a motorhome. Little crimes pop up along the way and Monk can't resist getting involved. Nor can he help sensing a pattern that reveals the hand of a serial killer at work on this highway to hell.