The Battle of Ranskoor Av Kolos

On the planet of Ranskoor Av Kolos, lies the remains of a brutal battlefield. But as the Doctor, Graham, Yaz and Ryan answer nine separate distress calls, they discover the planet holds far more secrets. Who is the mysterious commander with no memory? What lies beyond the mists? Who or what are the Ux? The answers will lead the Doctor and her friends towards a deadly reckoning.