The Doctor knows something is wrong, as the monsters do not appear to be the product of a normal evolutionary process. He traces an interference signal to the abandoned lighthouse on Black Island. Exploring the island with an eccentric local woman, Bronwyn, the Doctor finds an 'interstellar space-hopper' and, in the lamp room of the lighthouse, a psychic transmitter/receiver. Understanding that this is causing the children's nightmares, in turn realising the monsters they dream about, the Doctor is reluctant to dismantle the machine and risk damaging the children. He cannot reach the controls of the telepathic circuits as they are underneath the machine.