Before the war starts, Ned is resigned to a future working in the family funeral parlour. Then the covert operations at Bletchley Park begin and his life is transformed.

Ned and his mother leave Bletchley Park on a vital wartime mission into the remote Welsh countryside. Their task: to protect the priceless artwork that is being stored in a slate mine in the village of Manod. As long as its whereabouts are secret, they'll keep the national treasures out of the hands of the enemy.

But when it appears that someone in the village is trying to expose the truth, suspicion turns to the newcomers - Ned, his mother, and a young Jewish refugee, Anni. Can Ned, Anni and their friend Harri prove their loyalty to the mission and keep the secret safe?