Millions of years ago, the noble Ice Warriors fled to Deimos, moon of Mars, hoping to sit out the radioactive death throes of their home planet. When the TARDIS lands on Deimos, the Doctor discovers that the Warriors' ancient catacombs are now a popular stop for space tourists.

But the Martian dynasties are more than history, and the Warriors are far from extinct. It's not for nothing that 'Deimos' is the ancient word for 'dread'…