The world's most priceless artifacts--from hand-drawn maps to custom-forged armor to carved whale-bone knives--are protected in the Museum In-Between. But now someone is intent on destroying the Museum, and only thirteen-year-old Theo Garrison can stop them.

The Museum In-Between is a wondrous place, where clockwork figures pieced together from relics wander freely through the corridors, and creatures peeled from paintings are brought to life to serve as companions to those lucky enough to step through the magical portal. Each year, dozens of children are selected to join the ranks of the Museum staff to learn how to collect and protect priceless artifacts brimming with Musea, the essence of inspiration itself, including Viking-era ships, covered wagons from the American West, and a 2,000-year-old sarcophagus from ancient Egypt.

When the Museum's Head Curator arrives to personally recruit Theo Garrison, Theo has a lot of questions. Especially about the fate of his mother, who had been "Reliqued"--transformed into an artifact as punishment for attempting to sabotage one of the Museum's four sacred Pillars.

Only Theo and his father know the truth: Gloria Garrison is still alive and trapped somewhere in the Museum. Determined to save his mother, Theo accepts the invitation. What he finds is a mystery that reaches from the highest tower to the lowest dungeon, with spies and secrets around every corner. With new friends by his side and enemies lurking in the shadows, Theo must learn to master a rare, forbidden power he doesn't fully understand before it's too late.

Because the real danger never left the Museum, and someone is counting on Theo to finish what his mother started. Someone who believes that the most powerful thing isn't the ability to inspire--it's the ability to destroy.