New companion Bill Potts joined the Twelfth Doctor's comic adventures! But she got more than she bargained for when they bumped into a group of questing Vikings in the Ninth Century... Something has fallen to Earth, and is killing the Vikings one by one. The Doctor and Bill have met these invaders before, on Mars - the Ice Warriors! But these Ice Warriors have been infected by Mars' other dominant lifeform - the sentient virus known as the Flood!