When intelligence agents around the world come under attack from alien forces, MI6 turns to the only person who can help- a certain Doctor and her companions. As they travel the globe in pursuit of answers, threats arrive from all sides, leaving Earth’s security resting on the team’s shoulders. But where will this planet-threatening conspiracy lead them?

As Graham, Yaz and Ryan return home to see friends and family, they find themselves haunted by very different experiences. Who is the figure calling from beyond the stars for help, and why? And what are the fearsome Chagaskas terrorising Aleppo in 1380? To find the answers, Team TARDIS must embark on a mission which forces them to face their darkest fears.