The Outcast had saved the worst for last.
Mission Atomic is the fourth and final book in the fourth series of The 39 Clues, Doublecross.
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 Outcasts 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.
- Been There, Shaped History: Nathaniel Hartford was the one who instigated the Chernobyl disaster.
- Break His Heart to Save Him: Amy is forced to fake her own death in front of a video chat of Dan, in order to conceal Alek's turn to the good guys.
- Call-Back: During the Cahill party that is thrown at the end, Fiske appears, sporting his "El Coyote" persona, and wowing the audience with his dance moves.
- Curb-Stomp Battle: Alek is able to take down Amy, Jonah and Hamilton at the same time, with nothing but a silenced pistol and self-defence tactics.
- Dance Party Ending: A party is thrown at the Cahill mansion after the Outcast is defeated. Everyone but those who sided with the Outcast was invited.
- Even Evil Has Loved Ones: Alek actually had a wife, Natalia, who gave her life in reducing the effects of the Chernobyl disaster.
- HeelFace Turn: Alek receives this, after Amy convinces him that since Nathaniel caused the Chernobyl incident, he is partially responsible for the death of Alek's wife.
- Heroic Sacrifice: In a confined room, Alek, Amy and Dan are covered in Nathaniel's genetically-altered bees, ones that will kill Cahills with its sting. Alek then runs towards the nearest window to open it and lower the temperature for the bees to sleep and die. Unfortunately, his movements mean that the bees sting Alek to death.
- Hoist by His Own Petard: Nathaniel altered the genetic structure of bees to sting and kill all Cahills, to exact his revenge towards his former family. He dies when he, in a fit of panic, opens his observation deck to call his guards to stop Alek from lowering the warm room temperature that the bees sorely need. As a result, his observation deck is the only area that has the right temperature for the bees, so the insects swarm him and end his life.
- How We Got Here: The prologue begins at the middle of the story, where Dan is frantically communicating to a beaten Amy. On Amy's side, there is a gunshot, and Alek picks up Amy's phone and tells Nathaniel, who is on Dan's side of the line, that Amy has been executed. The rest of the book then jumps back three days ago and leads up to that very point.
- If You Kill Him, You Will Be Just Like Him: Dan is about to kill Alek with a submachine gun, as he believes Alek killed Amy, but eventually decides that he is better than that.
- Nuclear Nasty: This is what happened to one of the bears experimented on by Nathaniel, as it transformed into a vicious, horrendous beast. It severely wounds Sammy and tries to kill Nellie when the two visit the old Black Forest laboratory.
- Your Days Are Numbered: Alek ends up receiving a scratch after unblocking the Shanghai nuclear reactor pipe. Since the pipe was filled with radioactive water, he spends his last days to stop Nathaniel. Ironically, it's not the radiation poisoning that claims his life.