Welcome to Calderwood, a country home with one occupant, one maid, and one door that leads to a secret underground realm where something monstrous waits.

Arlo Reade comes to Calderwood in the summer of 1895 as a maid of all work and finds that she is, in fact, the only maid. The house is otherwise empty except for its owner, Tristan Calder, whom Arlo finds instantly captivating despite his odd habits and inconsistent personality. But Tristan's not the strangest thing at Calderwood. Following her curiosity into the pitch-black cellar, Arlo finds a door covered in intricate carvings of writhing snakes. At least, she thinks they're carvings-until one of them speaks. It says it'll open the door for her, if she solves the riddle of the three things it requires as payment.

Once she cracks the puzzle, Arlo finds a world where the house is backwards and as full of guests as Calderwood is empty. She also finds Lucien, the handsome, charming host who invites her to return three times. Arlo can't seem to quit Lucien and his glittering world, even as her affection for Tristan grows. But the third time is for keeps, and when she finds herself trapped in Lucien's house, Arlo has one chance to win her freedom and get back to Tristan and the world above before it's too late.