On the morning of 19 April 1956, Commander Lionel ‘Buster’ Crabb (RN retired) carried out a spying mission for MI6 under a visiting Soviet warship In Portsmouth Harbour. The dive went disastrously wrong. Crabb did not return from the dive. A cover-up was hastily attempted. Daily Mail reporter, Peter Marshall was the first to expose the deception. A media frenzy ensued. The government imposed an immediate embargo on disclosure of the facts. There is nothing more certain to fuel speculation than the suppression of information and it inevitably led to a plethora of theories about what happened to Commander Crabb. Interest in the incident was reignited when the embargo was extended by a further 50 years. We can anticipate full disclosure in 2056. What actually happened? Why did it deserve such secrecy? This books attempts to answer these questions. Without an official account of the covert operation and consequent events, speculation continues to fuel the mystery.