Young Galwyn Varianus is unhappily serving as a cabin boy on his uncle's ship when he meets Lord Artos, who is on his way, with two of his Companions, to the horse fair at Septimania. There he hopes to purchase horses big enough to carry armed warriors into battle, for Artos is convinced that such horses would give him an unbeatable advantage over the Saxons.

Galwyn has a great facility for languages and a love of horses. When Artos proves to be both kind and generous, unlike Galwyn's uncle, Galwyn runs away to join Artos' party. His love of horses quickly makes him indispensable and assures him of a place in Artos' retinue but, while working with the horses, Galwyn manages to make an enemy, though he makes far more friends. An experiment with "horse sandals" leads to Galwyn becoming one of Britain's first farriers.

Black Horses for the King is an interesting departure from most Arthurian-themed works. For one thing, Arthur (Artos) is a secondary character. The time is early in Arthur's career; there is no Guinevere, no Lancelot and no Merlin. In fact, there is no mention whatsoever of some of the more fantastic elements of the Arthurian saga. Excalibur is mentioned only in passing and as part of the scenery -- propped against a wall! No, Black Horse for the King is a story about a young man growing up in perilous times which just happen to be the beginning of King Arthur's reign.

Black Horses for the King is an interesting book with a well-told tale, but it is a tale that McCaffrey has told many times before, most notably in Dragonsong. Many of the situations Galwyn finds himself in can be compared to Menolly's adventures. Menolly also runs away, is given an apprenticeship she wants desperately and then alienates her peers because of her talents, while at the same time earning the respect of her elders.

So, while it is a most interesting variation on the Matter of Britain, and an excellent historical (and horse-storical!) novel, it doesn't break any new ground. Still, it makes an entertaining afternoon's reading.