From ancient Syria to present day Sheffield, and out into the wilds of space, something is stalking the Doctor and her friends and infecting people's nightmares. 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 embark on a mission that forces them to face their darkest fears.