Mission Atomic is the fourth and final book in the Doublecross series. 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.