Mission Hindenburg is the second book in the Doublecross series. It was written by C. Alexander London.

Official Synopsis


The Cahills are the world's most powerful family, but their strength is being tested. A sinister man calling himself The Outcast has targeted the family and set them an impossible test. He's recreating four of history's worst disasters and challenging the young Cahills to find and stop the tragedies before it's too late. Now, with one disaster behind them, siblings Dan and Amy Cahill and their friends have just days to discover what the Outcast's next move will be.

Their frantic search seems to be pointing toward a terrifying air disaster, the explosion of the Hindenburg airship. But no one travels by airship anymore -- what do the Outcast's cryptic messages mean? The young Cahills must split up and take to the skies to try to find the answer . . . before their whole world comes crashing down.


  • The second book in The 39 Clues series to feature a sky transportation vehicle on the cover, the first being In too Deep.


  • Book Cover Puzzle - (Pigpen Cipher) -​ House of Orange
  • Blimp Page Puzzle - (Pigpen Cipher) - hope is the answer
  • 39+ Pages Puzzle - (Caesar Shift) - til death do us part, which is a part of marriage vows and a clue to the identity of The Outcast.


The following cards will only be available as digital cards:

Card 341- Grace's Guidance

Card 342- Sabotaged!

Card 343- Burning Truth

Card 344- Father's Footsteps

Card 345- Decoding Flashes

Card 346- Family Tree - the back of the card is a part of The Outcast Master Plan Puzzle


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