It’s a self-assured author who decides to write a children’s novel about the adventures of a “young boy wizard” in a world of magic, but then Cressida Cowell has reasons to be confident: 8m copies sold of her How to Train Your Dragon books, a film franchise and a spin-off series for TV.

As with the Viking world of Dragon, the eagerly awaited The Wizards of Once is set in the ancient past and our two heroes are scrappy kids struggling with that timeless issue of failing to live up to parental expectations. In place of dragons, there are sprites, deep-thinking giants, ogres and snow cats living in an enchanted wildwood.

The kingdom of Wizards is at war with the neighbouring queendom of Warriors, against whose iron weapons the wizards’ magic is useless. When the boy wizard, Xar (a troublemaking prince waiting in vain for his magic to “come in”), meets the warrior princess, Wish, they discover that the evil magic of witches – long thought extinct – has returned.

The detail of Cowell’s imagined world is a delight, not least in her scratchy pencil illustrations that evoke the darting, insect-like sprites or the pitch-black terrors of the forest. And her kinetic prose barely pauses for breath as Xar and Wish leap from one action-packed scrape to the next (you can practically see the scenes from the already-signed Dreamworks film jumping off the pages).

In an introduction to her new series, Cowell (an advocate for kids literacy) extols the joys of being read to as a child and there are many pleasures here for parents, including Game of Thrones echoes (iron invaders, infectious “bad” magic) and a nice joke in which Crusher the giant ponders the paradoxes of an expanding universe (“giants are big and they tend to have BIG thoughts”). This one will run and run.

• The Wizards of Once by Cressida Cowell is published by Hodder (£12.99). To order a copy for £11.04 go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99