A cast-off soldier, lowered into a witch's dry well and left there to die, lights his pipe at a strange blue flame — and out of the smoke rises a servant no taller than a child and black as the coal it came from. The record keeps a single witness at this address, the Grimms' Household Tales (collected 1812–1857), where it is told as The Blue Light. When the smoke "had circled about the cavern", "a little black dwarf stood before him" and asked, "Lord, what are thy commands". The bond is absolute: "I must do everything thou biddest me", the little man says, and from then on each time the soldier "lit it at the blue light" the spirit is at his side — leading him up out of the well, carrying the king's daughter to him in her sleep, scattering peas through the streets to spoil her father's tracking, and at the last felling the false judge on the road to the gallows.

What the tale gives the helping spirit is a small, dark, biddable body — "the little black mannikin", the smoke's own child, summoned and dismissed by a pipe. It is a shape drawn straight from the hearth: the servant of the flame arrives in the colour of soot and the stature of a boy, and does murder at a word.

Thompson files only this one German tale beneath the address, so the spirit's kin in other traditions go unnamed on our shelf; the whole marvel rests on a single blue light in a single wood. Why, when a frightened imagination gives the helping power a body, should it come out small and dark — the size of a child, the colour of the coal from which it was conjured?