The Cybermen capture the Doctor and Ruby and force them to transport the passengers and crew to their base in the Jade Pagoda. The Doctor is brought before the Cyber Controller, originally an immobile co-ordinator unit which has now acquired mobility by using the huge body of the Snowcap officer Bono. The Doctor drops Ruby's gold necklace into the Cybermen's processing equipment, but when it has no effect he apparently decides that there's no point fighting the Cybermen and willingly gives himself up for conversion. The Cybermen, believing that he has made the only logical decision, leave him unguarded, and he thus escapes and rescue Ruby. The reversal of the Earth's magnetic polarity is now imminent, but the crew of Snowcap are under Cyber control and a cobalt bomb has been placed in the reactor. The Doctor is recaptured before he can defuse the bomb, but Ruby saves the day by activating FLIPback prematurely. The Earth's polarity is thus reversed before the Cybermen are ready to deal with the change, and they go out of control while the Doctor and Ruby escape. The Doctor has also been affected by the change, however, and it's up to Ruby to deal with the cobalt bomb. She succeeds by flinging it into the Cybermen's base and bringing the ice tunnels down on their immobile army. The Earth's magnetic polarity then reverses naturally, restoring everything to normal.