The Doctor and his companion, Clara, are on the most beautiful train in history, speeding past the stars of the future. But something terrible is killing the passengers. After you see the mummy, you only have 66 seconds. Then you die.
Alone, without the Doctor, Clara discovers a new danger from another dimension. But how do you hide when even the walls give no protection? People need help and the Doctor can’t leave the TARDIS. And Clara has to fight an enemy that can’t be seen.