It is 1914, and Thomas Maggs, the son of the local publican, lives with his parents and sister in a village on the Suffolk coast. Then one day the architect Charles Rennie Mackintosh arrives, and together with his red-haired artist wife, they soon become a source of fascination and wonder to Thomas. Yet just as Thomas and Mac's friendship begins to blossom, war with Germany is declared. The summer guests flee and are replaced by regiments of soldiers on their way to Belgium, and as the brutality of war weighs increasingly heavily on this coastal community, they become more suspicious of Mac and his curious behaviour.