A world-famous cryptographer has vanished without a trace. She spent years creating an unbreakable security system – and now, in a cruel twist of irony, unlocking that system is the only way to find her.

Witness statements from those closest to her reveal someone who was paranoid and very well connected – but what was she hiding? When a secret file marked ‘X’ is discovered, it opens with a simple message: ‘The secret code is not ***’. Within the folder is a list of names and 12 cryptic clues. Somewhere among 30,000 possible codes lies the one sequence that unlocks the truth – and where she may be.

But here’s the catch. Each clue reveals not what the code is, but what it isn’t. Using logic, deduction and a trail of increasingly revealing clues, you’ll eliminate thousands of possibilities, narrow the field and uncover the only code that fits every piece of evidence.

With 30,000 codes and just 500 words, your only code is to find the correct code. Can you follow the clues, crack the case and reveal the secret cipher before it’s lost forever?