39 Clues

The two siblings are mainstays throughout the series, spanning over a dozen books and boasting an array of authors for each book – every book has a different author. The impressive list of writers for this series includes Peter Lerangis and Rick Riordan. The ’39 Clues’ books also have 5 spin off series – Cahills vs Vespers, Rapid Fire, The Cahill Files, Unstoppable and Doublecross.