When 11-year-old April joins a group of kids living at Winterborne Home she doesn't expect to be there for very long. But she soon learns that this home isn't like any of the others - especially when she unearths the secret of the missing-and-presumed-dead billionaire, Gabriel Winterborne, who is neither missing nor dead but is actually living in a basement lair, sharpening his swords and looking for vengeance. Now that April knows Gabriel Winterborne is alive, she must turn to the other orphans to keep him that way. As a looming new danger threatens to take Gabriel down once and for all, they must use their individual talents to find a way to make sure this home for misfits isn't lost to them for ever. Because at the Winterborne Home, nothing is what it seems, no one is who they say they are and nowhere is safe. And now a ragtag group of orphans must unravel the riddle of a missing heir, a supposed phantom and a secret key, all without alerting the adults of Winterborne House that trouble is afoot.

Five orphans. Two sword-wielding vigilantes. One mansion. No rules. April thought she had her happy ending. After all, she has her new house and new friends and new guardian. But she also has a very big new secret. The kids of Winterborne House are the only ones who know that Gabriel Winterborne—famous billionaire and terrible cook—is really a sword-wielding vigilante. What they don’t know is that he’s not the only one. When a masked figure breaks in, looking for something—or someone—it’s clear that Gabriel has met his match, and now no one is safe. April and her friends will have to solve a decades-old mystery in order to hang on to the most important thing in the world: each other.