Near the end of The White Mountains, Will and his friends discover that he has been implanted with a tracking device, and that the Tripods are deliberately allowing him to escape so they can track him to the Free Men's base. This explains how the Tripods always seem to be around in the distance, despite spending many hours out of sight. Beanpole removes the device and the Tripod, realizing that they can no longer track Will electronically, attack. The boys are initially taken aback because of the Tripod's enormous size, but they remember an "explosive egg" they found in the ruins of the city. This is a grenade, and they manage to throw it into an opening in the Tripod. Without interior defenses, the Tripod is destroyed, and the boys continue traveling to the White Mountains, where they will find help and others to fight the Tripods.