Florian is 12 years old and has just moved to Washington. He's learning his way around using TOAST, which stands for the Theory of All Small Things. It's a technique he invented to solve life's little mysteries. But when he teaches it to his new friend Margaret, they uncover a mystery that isn't little. In fact, it's huge, and it involves the National Gallery, the FBI, and a notorious crime syndicate known as EEL. Can Florian decipher the clues and finish his homework in time to help the FBI solve the case?

Sara Martinez is a hacker. She recently broke into the New York City foster care system to expose her foster parents as cheats and lawbreakers. However, instead of being hailed as a hero, Sara finds herself facing years in a juvenile detention facility and banned from using computers for the same stretch of time. Enter Mother, a British spy who not only gets Sara released from jail but also offers her a chance to make a home for herself within a secret MI5 agency. Operating out of a base in Scotland, the City Spies are five kids from various parts of the world.

Ben Ripley may only be in middle school, but he's already pegged his dream job: CIA or bust. Unfortunately for him, his personality doesn't exactly scream "secret agent". In fact Ben is so awkward, he can barely get to school and back without a mishap. Because of his innate nerdiness, Ben is not surprised when he is recruited for a magnet school with a focus on science - but he's entirely shocked to discover that the school is actually a front for a junior CIA academy.

Like his fellow lunarnauts - otherwise known as Moonies - living on Moon Base Alpha, twelve-year-old Dashiell Gibson is famous the world over for being one of the first humans to live on the moon. And he's bored out of his mind. Kids aren't allowed on the lunar surface, meaning they're trapped inside the tiny moon base with next to nothing to occupy their time - and the only other kid Dash's age spends all his time hooked into virtual reality games.

Kyle Keeley is the class clown, popular with most kids, (if not the teachers), and an ardent fan of all games: board games, word games, and particularly video games. His hero, Luigi Lemoncello, the most notorious and creative game maker in the world, just so happens to be the genius behind the building of the new town library. Lucky Kyle wins a coveted spot to be one of the first 12 kids in the library for an overnight of fun, food, and lots and lots of games. But when morning comes, the doors remain locked.