 Tracing the source, the Doctor takes them to Ynys Du, a small village on the Welsh coast.They discover that the villagers are terrorised by fantastical monsters which roam the streets and woods at night; the adults are anxious and the children all have nightmares.The trouble seems to have begun when an elderly Nathaniel Morton returned to the village after many years away and established a 'nursing home' in the old rectory.