Day of Doom is the sixth and final book in the second series of The 39 Clues, Cahills vs. Vespers.
It started with a kidnapping. A shadowy organization known only as the Vespers snatched seven members of the Cahill family and demanded a series of bizarre ransoms from around the world. Thirteen-year-old Dan Cahill and his older sister Amy began a global treasure hunt, determined to bring back whatever Vesper One needed, so long as it kept the hostages safe.
But when they deliver the last ransom, Amy and Dan discover Vesper One's terrifying endgame. The objects he demanded are vital pieces in a Vesper plot that will harm millions of innocent people. Now the two siblings and their friends are in an all-out sprint to stop Vesper One... before the whole world goes BOOM.
Tropes:
- Anyone Can Die: Let's say this trope rears its ugly head for this instalment, even though it has happened occasionally in the second series. Natalie Kabra, Evan Tollier, Damien Vesper III and Isabel Kabra all bite the bullet by the end.
- Cruel and Unusual Death: Damien Vesper III finally puts in Gideon's ring into the Machina Fini Mundi, and it activates... just as a Master Serum-infused Isabel pushes him into it. He ends up being crushed between the gears, kicking and screaming all the way, and his body melts afterwards.
- Roaring Rampage of Revenge: Isabel goes on one after her daughter, Natalie dies. She does this by drinking Dan's Master Serum.
- Surprisingly Happy Ending: Despite all the doom and gloom that Amy and Dan went through due to the Vespers, every Cahill comes out happy and part ways towards their homes, the world is saved due to the Machini Fini Mundi being buried under tons of rubble, and the surviving Vespers (Casper, Cheyenne and Sandy) are arrested for multiple crimes, after attempting to escape in secret.
