In a quiet glen beyond the reach of the railway lives a peculiar family who knows the best magic is the kind found in ordinary moments.

When Ismay Gebhardt is dismissed from yet another teaching post after an unfortunate accident (which everyone survived!), she accepts a last-chance job as a private tutor in sleepy Glenmaidens village. The town is brimming with natural beauty, uncanny traditions, and earnest locals, none more unusual than her three young pupils—the Underhill sisters—and their puzzling father.

Determined to make herself useful after several catastrophic lessons with the unbiddable girls, Ismay writes to the transport bureau suggesting an extension to the train line, hoping to bring Glenmaidens into modernity. As usual, Ismay's good intentions lead to chaos with the arrival of the bureau's frustratingly thorough officer, Hamish Breck, whose railway plans threaten not only the glen's tranquility, but also the ancient oak tree at its heart. Amidst a mess of her own making, Ismay unearths Glenmaidens' enchanted secret: the Underhills, like many villagers, are fairies who settled in the mortal world in search of a gentler life, and the oak is their only bridge back to the moonlit realm of the fantastic.

As summer heat rises, Ismay schemes with her magical neighbors to prevent the extension, each day finding herself more entangled with the charming, persistent bureaucrat. With her newfound family, the way between worlds, and her heart all at risk, Ismay must decide how much she would bargain to finally embrace the wonder and belonging she's always wished for.