From the publisher:
When a stranger from the past arrives in the middle of the night with shocking news, Jack, Annie, and Davey are catapulted into the wildest adventure they’ve ever had. Their parents have been arrested on suspicion of being spies. Not only in a different country but in a different time—Prague, 1903. The children travel back in time and find themselves face to face with danger, mystery, and the magic of a strange place. Where are their parents and who has stolen the key to the time machine? Will our young heroes be in time to save their parents from siniser Karlstein Castle? And even if they do, how will they return to the present day without the key? Alchemists, mythical creatures, and a man with a hook for a hand hold the answers they’re looking for.