The 39 Clues: Doublecross #4 Mission Atomic

Thirteen-year-old Dan Cahill and his older sister, Amy, are running out of time. An exiled Cahill known as the Outcast has already recreated three of history’s worst disasters, and he’s saved the worst for last. If Dan and Amy can’t find and stop the Outcast fast, he will initiate a full-scale nuclear meltdown. But as Dan and Amy race around the world, they discover something horrifying. The Outcast’s disasters are only a smokescreen to cover up his true plan, a diabolical revenge on the family that betrayed him. Soon Amy and Dan will have to confront a hard truth: sometimes the only way to save the world is to sacrifice everything you love.