Helia was basically abandoned by her parents, but she keeps this information on the down low. She doesn't really have a lot of options, so she's going to live in a foreign country with an uncle she hasn't seen since she was a toddler. Worse, he's barely ever at home. Fortunately, despite having a culture shock, she makes friends easily in this small town of Lucrest.
Early on, Tessa dares her to sleep in the haunted shopping center overnight. It turns out the place has a strict curfew with rumors of strange lights, sounds, and slime monsters bubbling up from the ground. Helia finds that to be true and more, stumbling upon an entire dungeon beneath the city, populated with multiple fantasy races and nations. There's dark secrets and political intrigue and all that, but her most mysterious recovery is an abandoned horned boy with otherworldly powers - Rune.