When strange late-night letters start arriving at home, Emily's parents set off to investigate. But when her parents disappear completely and Emily is left home alone to face the weird strangers that begin to appear at her door, she takes all of the clues at her disposal and makes for the place where the letters came from—the mysterious Night Post. What she'll discover is the secret world of the Midnight Hour—a Victorian London frozen in time, full of magic and monsters. Kept safe by an age-old agreement, the Night Folk have been exiled to a parallel world that can only be accessed by a selected few, including the mail carriers of the infamous Night Post that operate between the two worlds. Emily's parents are key players in keeping the Night Folk safe, but when the division of the two worlds is threatened, Emily must search for her parents while navigating this dark and unknown version of London. Armed only with a packed lunch, her very sleepy pocket hedgehog, and her infamously big argumentative mouth, she must escape bloodthirsty creatures of the night, figure out her own family secrets, and maybe just save the world.

Emily must battle the greatest evil that has threatened The Midnight Hour. Can she keep its magic from leaking into the real world? They must have come from under beds, out of mirrors, up from caves, and down from attics, all out of the darkness and into the moonlight. They were the Night Folk, and this was their world. Now that Emily knows that her blood ties her to The Midnight Hour, she feels more connected to this frozen pocket of time than ever. But not only does she have to come to terms with her new identity as a Pooka, her parents also had to go and have another baby. And how weird is that? Life is feeling frustrating from all angles... But when Emily begins to encounter strange happenings within The Midnight Hour, her worst fears are confirmed: there is a hole in the Hour and it is leaking magic. Whoever is going through it is making the tear worse and worse, posing a threat to the survival of the whole world. With Emily's parents distracted with the new baby, it's up to Emily to find the hole and help fix it.

Emily and Tarkus are back again in one last adventure to save the Midnight Hour. Their old adversary, the Nocturne, is determined to destroy their beloved magical world and everyone in it. With the added peril of the villainous Hunt, whose mission it is to Make Britain Dark Again, the barrier between worlds begins to glitch and fade. Emily might just have a plan to save all worlds, but she's going to need everyone to help....