A King's Ransom (The 39 Clues: Cahills vs. Vespers, Book 2)

Thirteen-year-old Dan Cahill and his sister Amy are plunged into a high-stakes race against time to rescue their kidnapped family members from the shadowy organization known as the Vespers. With an impossible ransom demand at stake, the siblings must track down a long-lost ancient map, leading them through a web of historical intrigue involving Nazis, spies, and dangerous secrets. As the clock ticks down, each decision they make could mean life or death for their loved ones.