The Frozen Earth

"The Frozen Earth" is the fifth episode in the eighth season of Doctor Who, set back on Earth in present day where Doctor Edward Bradley and his team have discovered several frozen bodies in Antartica, unwittingly reviving the Ice Warriors, an old foe of the Doctor. It is continued from Mars and Venus as the Ice Warrior's execute their plan to freeze the Earth so they can build a vessel to help them go back to Mars, which they do not know has been devoid of Ice Warriors for years.

Synopsis
As the Earth rapidly freezes, the Doctor and Billy struggle to defeat Commander Izaryx and his Ice Warriors. With the help of Doctor Isabella Cartwright, the Doctor and Billy foil their plan by destroying the restored Ice Warrior ship, and Izaryx and his men are destroyed with it. The Earth returns to its normal state, and the Doctor invites Isabella to join him the TARDIS, but will she accept such a task?