From the depths of Space a new foe rises to do battle with mankind: the British Space Empire is threatened by the lemming-people of Yull, ruthless enemies who attack without mercy, fear, or any concept of self preservation. At the call of their war god, the Yull have turned on the Empire, hell-bent on conquest and destruction in their rush towards the cliffs of destiny. When the Yullian army is forced to retreat at the battle of the River Tam, the disgraced Colonel Vock swears revenge on the clan of Suruk the Slayer, Isambard Smith's homicidal alien friend. Now Smith and his crew must defend the Empire and civilize the stuffing out of a horde of bloodthirsty lemming-men—which would be easy were it not for a sinister robotics company, a Ghast general with a fondness for genetic engineering, and an ancient brotherhood of Morris Dancers—who may yet hold the key to victory.