The word “treacle” has a long history in English. Before it denoted a by-product of sugar manufacture, it was understood as a healing substance, deriving from an Ancient Greek word for an antidote to snake venom; its archaic doublet “theriac” still has that meaning. Chaucer’s cheery Host, Harry Bailly, claims to be so moved by the Physician’s tragic tale that he fears he will have a heart attack, unless he can get some “triacle” – medicine – or, failing that, “a draught of moist and corny ale”. For Truth in William Langland’s Piers Plowman, “love is triacle of Heaven”, healing all things. And so, too, Treacle Walker, the title protagonist of Alan Garner’s allusive new fable, can heal “all things. Save jealousy. Which none can”.

Garner’s story is short but profound. The rag-and-bone man Treacle Walker pulls up his white horse and cart at the house where a boy, Joe Coppock, lives alone, marking time by the passing of Noony, the midday train. Treacle is in the business of exchange: rag and bone (Joe’s old pyjamas and a lamb’s shoulder-blade) are swapped for a donkey stone, used for whitening front steps, and the choice of a treasure from Treacle’s chest. Joe’s selection of a pot of strange ointment and his invitation to Treacle to come inside and sit in the chimney space with him sets off a chain of mysterious happenings that seem both inexplicable and inevitable. During that first conversation in the chimney, Treacle Walker plays a tune on a human shin bone, “a tune with wings, trampling things, tightened strings, boggarts and bogles and brags on their feet; the man in the oak”. This tune awakens legendary powers and the potent rituals of the past. When Joe plays in his turn, he summons up the cuckoo, harbinger of summer, whose insistent cry echoes through the story.

Joe has a “lazy eye”, and thus must keep his good one covered up to train the other to adjust. Accidentally smearing Treacle’s ointment on to his good eyelid, Joe can suddenly behold a very different world, a “knacky” reality that can be glimpsed alongside his own. He has fallen under “the glamourie”, he learns, for this is the magic ointment of traditional folktales; it enables humans to perceive the fairy. A savage price is often exacted for that vision.

Joe uses the donkey stone on his threshold to...