Mission Atomic (the 39 Clues: Doublecross, Book 4)

The story follows thirteen-year-old Dan Cahill and his sister, Amy, as they race against time to thwart an exiled family member known as the Outcast. This villain has resurrected some of history's most catastrophic disasters and plans to unleash a nuclear meltdown. With the clock ticking, the siblings must use their wits and courage to prevent a catastrophic event that could change the world forever.