Get ready to be spellbound by the new, fantastical novel from the Sunday Times bestselling author of fantasy sensation The Book of Doors.

The world of unknowable objects—magical items that most people have no idea possess powers—has been quiet for decades. But three current members of a secret society have remained watchful, meeting every six months in the basement of a bookshop in London. They are pledged to protect their archive of magical items, hidden away and safe from the outside world—and to keep the world safe from them.

When Frank Simpson, the longest-standing member of the Society of Unknowable Objects, hears of a new artefact coming to light in Hong Kong, he sends the Society’s newest member, author Magda Sparks, to investigate. Within hours of arriving, Magda is facing death and danger, confronted by a professional killer who knows all about unknowable objects—especially one stolen from him a decade earlier. Forced to flee, Magda uses an artefact that not even the rest of the Society knows exists.

Back in London, Magda soon learns hers is not the only secret being kept. And the most dangerous secret may concern the true purpose of the Society itself. Her discoveries send her on a perilous journey across the Atlantic to the Deep South of the United States—not in pursuit of an unknowable object, but an unknowable person: the killer she first encountered in Hong Kong.

As Magda uncovers more, she realises that others are also chasing these magical items—and that her own family’s legacy is deeply entwined in the secrets surrounding them. Magic has always been too powerful to reveal to the world. But Magda will learn that something even more powerful may be waiting: the truth.