Caroline: A Mystery, By Cornelius Medvei

As he nears retirement, Mr Shaw the insurance broker goes on his summer holiday and falls for a creature with "eyes a man could drown in". Their "strange affair" begins with a shock of mutual recognition in a field: "two strangers come face to face" and "an overpowering force shakes them". Shaw takes his new-found beloved back to the family home, an object of "devotion" as much as "affection". She wins over office colleagues, when she comes into work, with her "lovely personality". Her staff assessment promises swift promotion."Always well-groomed and never over-dressed", she also learns to play chess with a grandmaster's eye and a killer instinct. Her gift shows off "the grace of a dancer, the force of a juggernaut". Yet, for all her allure, this angelic being keeps a distance: "She combined great personal charm with an air of serene detachment". Then, one sad night, Caroline nudges open the door of her makeshift stable in Mr Shaw's backyard and disappears for ever.

Caroline is a donkey. Blending "strength and delicacy, crudeness and refinement", she seems, like all her kind, to have been "assembled from a box of spare parts". We hear Shaw's, and her, story at second-hand. It reaches us via a bulging package of old documents, some reproduced here in facsimile, and his son's yarn. He tells it to a journalist friend, after Shaw senior's death, in a humdrum café by the docks of a fast-expanding river port. Shaw, the dreaming drudge, strums "House of the Rising Sun" on a guitar in his vacation cottage in the northern hills. Later, he takes Caroline to see an al fresco screening of Audrey Hepburn in Roman Holiday (she causes mayhem in the park). Yet the city where this tale unfolds feels like some smoggy Asian boom-town, a climate confirmed by the blurred Chinese-looking snaps that (WG Sebald-style) punctuate the narrative. The principal humans have surnames that could be either Western or, losing a letter, Chinese: Shaw, Low, Young, Lamb.

Subtitled "a mystery", this novella remains one to the end. It is also a complete delight. In literature east and west, the beast fable dates back over millennia. Cornelius Medvei, who wrote in his debut Mr Thundermug about a baboon who also part-joined human society, knows his genre well. Yet he never pens in Caroline with her allegorical ancestors. Forget Bottom and Titania. Shaw's chaste worship has nothing "scandalous or comic" about it. Rather, it restores pride and passion to a man who, in spite of respect at work and home, feels his life has come to nothing. Now his story glows with the grandeur of magnificent obsession: "like something out of the sagas, or the lives of the saints".

Medvei's sleek prose has all the serenity and dignity of his loveable heroine. That only makes Caroline funnier – but never in a way that disrespects her, or Shaw. In its sly humour, grave warmth and invitation to think, and feel, afresh, Caroline sounds more like the work of some delphic master from Kiev, Prague or Buenos Aires than of a youngish Londoner. And behind its beautifully measured tread lies that glimpse of a distant yet familiar city in which a chess-playing donkey might thrive in crowded alleys where ancient myth meets daily grind, and "the ordinary and the fantastic... are mingled everywhere you look".