On the run from the Time Lords and in serious need of help, the Doctor heads for 17th-century Russia in search of the legendary witch of Slavic folklore… Baba Yaga.

But while trying to gain assistance from this powerful entity, the Doctor finds herself embroiled in events from the most famous of Baba Yaga's tales when the tries to help a beautiful young woman called Vasilisa retrieve a burning ember to save her family from the bitter Russian winter. What is real? What is fantasy? And will the Doctor be able to tell the difference in time?