The hive of the Vrill bears the scars of a terrifying cataclysm.  Only a handful remain alive, hatched after the holocaust of the mysterious Winterlack.  The Vrill seek a new Authority.  They find the Doctor, a two-legged creature who can lead them to survival.  He must solve the mystery of the Carrion beast that haunts the lower chambers.  He must face the Winterlack that still stalk the mountains.  And he must find a path that does not lead to extinction...

Plus: Klein's Story
Elizabeth Klein is an anomaly.  A renegade from an alternate future in which the Nazis won World War II.  In an attempt to get to know his latest companion, the Doctor invites Klein to tell him how exactly she came to be in possession of his TARDIS and of the events that led to her trip into the past to Colditz Castle.