Secret Agent Jack Stalwart: Book 4: The Caper of the Crown Jewels: England

In The Caper of the Crown Jewels, Jack is summoned to solve a matter of grave national importance: the theft of the Crown Jewels of the British Empire from the Tower of London. Arriving on the scene, he is greeted by a traditional Tower guard- a Yeoman Warder (or Beefeater)- who explains what's missing: The Imperial State Crown, the Sovereign's Orb, and the Sovereign's Scepter with the cross containing the finest-cut diamond in the world, the Star of Africa.
Jack identifies Ivan the Incredible and his assistant, Jazz, as the thieves immediately--but puzzling out how they did it is stickier. The famous Tower has the most advanced security in the world, and even using his impressive gadgets (the Encryption notebook, Heli-Spacer, Rock Corer, and Rope Tornado) Jack is flummoxed by how the jewels were spirited out. However, Jack can conjure up more than gadgets--he foils the evil magicians with some powerful mojo of his own, dispels an invisibility enchantment, and narrowly avoids the executioner's block before restoring the jewels to the crown and earning the gratitude of the Queen herself!