The Doctor and Romana freeze and Kroll, unable to detect them, attacks the Swampie settlement. The refinery crew watch on the scanners and Thawn prepares to drop their next orbit shot onto the creature. Dugeen and Fenner warn against it, and Fenner notes the atmosphere is thin enough that the fireball could asphyxiate them. Thawn is intent on going ahead with is plan.
The Doctor and Romana enter the refinery. They arrive and listen as Dugeen objects on moral grounds. Thawn realizes that he’s a Son of Earth member and knocks him out. He draws his gun and Fenner has no choice but to obey and activate the countdown. The Doctor goes to the rocket silo to stop the launch.
The surviving Swampies retreat and Ranquin believes that Kroll is punishing them for letting the dryfoots escape. He insists it was a test and decides that they need to launch an attack on the refinery.
The Doctor enters the rocket silo and leaves Romana outside. She refuses to abandon him and tries to get him to leave because it’s too late. The Doctor ignores her and works on the controls. In the control center, Dugeen recovers consciousness and tries to stop the countdown. Thawn guns him down and the countdown continues. In the silo, the Doctor smashes a panel and stops the launch at three seconds. Thawn goes to fix it but Fenner reveals that Kroll has submerged and they can’t hit it while it’s underwater. Fenner plans to report Thawn for murder and Thawn goes to fix the ignition.
The Doctor blacks out from oxygen starvation and Romana wakes him. They leave the silo only to find Thawn outside. He doesn’t believe the Doctor’s denial and escorts them to the control center. Meanwhile, the Swampies enter the base and Ranquin declares it an abomination. He plans to ask Kroll to destroy it all, and Varlik wonders why Kroll would obey him. Varlik notes that Kroll destroyed their settlement but Ranquin stands by his religious obsession.
Thawn returns to the control center as Fenner clears away Dugeen’s body. Fenner reports that Kroll is approaching the refinery. The Swampie arrives and kill Thawn with an arrow, then grab guns and hold the Doctor, Romana, and Fenner at gunpoint. Ranquin prepares to kill them but is interrupted when Kroll attacks the refinery. Ranquin starts praying and Romana approaches a window. The Doctor yanks her back just in time as it smashes through the window. They seal the control center but warn it won’t last for long. The Doctor has Fenner turn on the processing centrifuge to distract the creature.
Ranquin believes that Kroll is responding to his prayers and goes off to see his god. He goes to the shattered pipe and calls out to the tentacle. Ranquin orders it to attack the dryfoots, but the tentacle grabs him and pulls him into the pipe.
The Doctor decides to test his theory. He takes the Tracer and goes out onto the platform. He approaches the side of Kroll but it strikes him with a tentacle, knocking the Tracer aside. Another tentacle grabs him and the Doctor struggles to grab the Tracer. He grabs it and touches Kroll… and the creatures disappears in a burst of energy. The Doctor is left holding the fifth segment of the Key of Time.
The Doctor returns to the control center and shows Romana the fifth segment. Fenner tells them that something is blocking the firing bay. The computer is preparing an automated orbital shot but Kroll’s rampage blocked the bay. They have no way to stop the computer. The Doctor cuts several wires without success, and finally short-circuits the power cables at the very last second. He tells Fenner that someone will come to rescue him and he should help the Swampies until then.
The Doctor and Romana depart for the TARDIS, and the Doctor explains that the symbol of power was the fifth segment. When Kroll swallowed it, the power of the segment caused it to grow to giant size.