“We don't get aliens in Sheffield.” In a South Yorkshire city, Ryan Sinclair, Yasmin Khan and Graham O'Brien are about to have their lives changed forever, as a mysterious woman, unable to remember her own name, falls from the night sky. Can they believe a word she says? And can she help solve the strange events taking place across the city?

On the edge of a Norwegian fjord in the present day, the Doctor, Ryan, Graham and Yaz discover a boarded-up cottage and a girl named Hanne in need of their help. What has happened here? What monster lurks in the woods around the cottage - and beyond?