In Mechanical, Walker continues tuning the modified radio while Shirly listens in alarm to strangers arguing over delivery schedules and an imminent cleaning. By marking strong signals on the potentiometer, Walker counts eleven other channels besides their own and becomes fascinated by the possibility that many other inhabited places exist beyond Silo 18. When Shirly notices the small circuit board is labeled with the number eighteen, she quickly concludes there must be at least that many silos, and the mention of a cleaning convinces both of them that the voices are coming from places like theirs. Shirly decides Jenkins must hear this immediately.

Before Shirly can act on that realization, a violent explosion shakes the room and knocks Walker to the floor. Dust rains down, his ears ring, and his magnifiers are shattered underfoot. Gunfire erupts outside as Jenkins hauls Walker up and tells him the enemy has breached their position and Mechanical is falling back. Harper helps the stunned Shirly while Jenkins calls for everyone to move.

Walker tries to tell Jenkins that he fixed the radio, but Jenkins bitterly answers that the success has come too late to stop the attack. As the fighting draws closer and more blasts shake the floor, Shirly insists they cannot abandon the radio because it proves there are other silos. Walker, dazed and reluctant, finally tells her to take the antenna, and she climbs onto the bench to pull it down while he tries to gather the essential components.

Faced with leaving the workshop he had sworn never to abandon again, Walker looks around at his possessions and chooses only what matters. He dumps out his parts bin, sweeps in the radio pieces, adds the transformer, soldering iron, and a few tools, while Harper shouts that they must go immediately. Shirly grabs Walker by the arm and pulls him toward the door, and Walker realizes that this time he truly is leaving his room as Mechanical retreats.