Jake, 11-year-old seasoned time traveler, opens his front door to his mentor. The long-lived Swiss alchemist bears bad news: Jake’s teenage mentor, Will, is missing.

Oh, no! Even worse: the alchemist wants to send Jake and his twin Ava to the Guardians of Time Guild headquarters to look for Will, while he checks out a rumor elsewhere. After an unsettling wait in 1529 Vienna at Headquarters, the twins learn that their nemesis Martin has kidnapped Will, and that their alchemist friend is stuck in Asia and can’t help them.

Jake and Ava are rookies. They’ve brought along their little cousin, their babysitting charge for the summer, and they have to keep her safe. How can they even figure out how to make the Headquarters time machine work? And now, cannonballs are falling! It’s the Siege of Vienna!

Book 3 of the Guardians of Time series.