While exploring the Ice Warrior catacombs, Harold and Margaret discovered a group of living Ice Warriors — one of them describing the group as "the last of our race", though as the Eighth Doctor pointed out to him, "there [were] some more of you frozen out in the asteroid belt" — took over a tourist shuttle, holding the tourists as hostages so they could take over the atmospheric re-ioniser on Deimos Moonbase, kill the human colonists and reclaim Mars. Harold secretly sent a distress signal to warn the base. The Doctor arrived to negotiate, but was shot non-fatally.
After the rocket took off, an artificial gravity eddy pulled it back down to Deimos. After forcing the Doctor to repair the re-ioniser, the Ice Warriors killed all 600 people on board the rocket with it — including Harold and Margaret — while testing to see if the Doctor had meddled with the device. (AUDIO: The Resurrection of Mars)