From the outset this story grips the reader with energy, vivid characterisation and a compelling economy of writing. We learn so much about who Jade, the protagonist is – and why – before the first page turns. Before the end of the chapter, we know her hopes and dreams, and just as clearly, we can see how her personal flaws and fears will be the biggest barrier to her achieving her ambitions.

Jade’s a mixed martial arts fighter living in New York who hopes to turn professional as soon as she turns 18. She isn’t cherishing some implausible fantasy. Sullivan portrays Jade’s place in this particular world with persuasive reality, not least because Jade herself is an uncompromising realist. She’s aware of the undercurrents of sexism in her chosen career, along with the financial and other pressures governing so many aspects of martial arts contests and films, often with unsavoury consequences.

Which is to say, she’s aware of these things in a wholly appropriate manner for a 17 year old. Sullivan never falls into that trap of portraying a teenager with a forty-something mindset. Jade’s world view, along with her impulsiveness, her occasional naivety and her grudgingly admitted vulnerabilities ring just as true as her relationships with her phone, with social media and with the opposite sex. Romantic relationships is merely one area where Sullivan writes with a refreshing lack of sentimentality about boys and girls alike who are still in the process of forming their own identity amid the pitfalls of peer pressure and social expectation. The book’s exploration of violence within pop culture is just as thoughtful, while the dramatic fight scenes are wholly convincing – of particular interest to me personally as a martial arts student for over thirty years.

Having spectacularly disgraced herself at her home gym, Jade is sent to Thailand to train for the summer, until the fuss dies down. Her culture shock is sympathetically portrayed without ever patronising that country or its culture. Nor does Sullivan gloss over problematic and frequently exploitative relationships between the First World and the Third. Here she shows clear appreciation for the teenage mindset’s virtues; most notably in Jade’s absence of and intolerance for hypocrisy and dubious compromise. It’s the corruption of adult greed, whether for sex, drugs or something far more sinister and fantastical, which now drives the plot forward with increasing intensity.

This unfolding combination of action-thriller and fantasy novel is handled superbly, especially when Jade has to cope with the consequences of collision between a mythic otherworldly forest’s denizens and cold hard reality. Now Sullivan brings the portal fantasy, which has been a staple of Young Adult fiction from EE Nesbit and CS Lewis onwards, right up to date. Mya, refugee from Myanmar, may be able to step from one world to another but if she’s caught in modern-day New York as an illegal immigrant, there’ll be no end of trouble. If the man who’s been exploiting her magical talents tracks her down, Mya and Jade alike face far more chilling dangers. Can they help the journalist who’s trying to blow the whistle on his real-world evil? At what cost to themselves and to innocent bystanders? All I’ll say is Sullivan pulls no punches as the narrative reaches its climax.

At 302 pages, this is a fast-paced and eminently readable story for all ages and all genders. The book’s available in paperback or ebook, from your local bookstore or preferred online retailer. If your local bookstore isn’t stocking it, draw their attention to it and if you have dealings with local or school libraries, do flag it up to their staff.