The Doctor is still being jolted through his own timeline, and has now found himself with Nyssa, Tegan and Adric in ninth century Iceland near a Viking settlement on the edge of a volcano. A settlement whose leader has just found a god in the ice.

The TARDIS crew are soon in a battle with the fearsome Ice Warriors. There are a lot of lives to save… and not just those of their new friends.

The Doctor’s about to find that his biggest battle may be with his own conscience.