The existential threat posed by the Skarasen—a Zygon bio-weapon creature—used as a lure and weapon against humanity, forcing the Doctor and UNIT into desperate countermeasures

The Doctor inspects a captured Zygon signalling device and theorizes it emits a primal mating call designed to lure the Skarasen toward human prey. Huckle’s firsthand account of hearing unnatural …

Stranded after his vehicle fails, the Doctor flees the pursuing Skarasen across Tullock Moor. Amid the chaos he detects a repeating signal and retrieves a tracking device from his pocket. …