The First Doctor and his companions are unaware that the planet is dangerously radioactive when the TARDIS arrives in a petrified rainforest. The Doctor is excited to investigate a futuristic metropolis discovered beyond the forest. Ian and Barbara are adamant about returning to the ship. Susan is separated from the rest of the crew on the way back to the TARDIS and believes she is touched by a human hand. Susan is disappointed that no one believes her, and Barbara complains about feeling ill when they return to the ship. There is a knock on the door from outside the TARDIS, but the scanners reveal no one there. As a result, Ian and Barbara demand that the Doctor remove them from this location. He appears to comply, but the Doctor, keen to get his way, destroy the TARDIS, stating that mercury is required for the fluid link. The only place where you can locate mercury is in the city.
When the travelers emerge from the TARDIS the following day, they discover a little metal box outside. It contains vials filled with an amber liquid, which was dropped by whoever knocked the night before. Susan places the box in the ship for safekeeping, and the four travelers depart for the enigmatic metropolis. It’s entirely made of metal, with doors designed like squat, rounded arches. The travelers split up. Barbara walks along with a series of corridors, closing doors behind her as she goes. She realizes she is imprisoned. A bizarre being appears, menacing her with a metal arm.