Nearly fifty years after the Second World War, two children uncover a secret whilst playing at an old shed. With secret codes, worries about whether someone they knew had been involved and many unanswered questions, Selina and William slowly discover the secret of Shed One. But danger lurks as the truth comes to light. So, who can they tell? And who can be trusted? Nearby Bletchley Park, home of the codebreakers during the war, may just hold the key. And maybe, just maybe, the ‘fishy secrets’ will finally be revealed.