Once, there were four worlds, nestled like pages in a book, each pulsing with fantastical power and connected by a single city: London. Until the magic grew too fast and forced the worlds to seal the doors between them in a desperate gamble to protect their own. The few magicians who could still open the doors grew more rare as time passed and now, only three Antari are known in recent memory—Kell Maresh of Red London, Delilah Bard of Grey London, and Holland Vosijk, of White London.

Kell is one of the last Travelers - magicians with a rare, coveted ability to travel between parallel universes. As such, he can choose where he lands. There's Grey London, dirty and boring, without any magic, ruled by a mad King George. Then there's Red London, where life and magic are revered, and the Maresh Dynasty presides over a flourishing empire. There's White London, ruled by whoever has murdered their way to the throne. And once upon a time, there was Black London...but no one speaks of that now.

It's been 297 days since David died - and came back. He may have survived the avalanche, but the aftermath has been far worse. His wife moved out, taking his son with her, and a devastated David hasn't left his house since, terrified of the mysterious new power that followed him home from the ill-fated expedition. After months in seclusion, David's ready for a fresh start, and ventures out, determined to keep his power in check. But David's power isn't the one he needs to worry about.

Olivia Prior has grown up in Merilance School for Girls, and all she has of her past is her mother’s journal—which seems to unravel into madness. Then, a letter invites Olivia to come home to Gallant. Yet when Olivia arrives, no one is expecting her. But Olivia is not about to leave the first place that feels like home; it doesn’t matter if her cousin Matthew is hostile, or if she sees half-formed ghouls haunting the hallways.

The Archive, an otherworldly library, contains the bodies of everyone who has ever died. But when the Archive is compromised from within, 16-year-old Mackenzie Bishop must use her skills as a Keeper to identify the traitor and prevent violent Histories from escaping into our world.