Thomas Maggs, the son of the local publican, lives with his parents and sister in a village on the Suffolk coast in 1914. He is the youngest child, and the only son surviving. Life is quiet - shaped by the seasons, fishing and farming and the summer visitors.
Then one day a mysterious Scotsman arrives. To Thomas he looks for all the world like a detective, in his black cape and hat of felted wool, and the way he puffs on his pipe as if he's Sherlock Holmes. Mac is what the locals call him when they whisper about him in the inn. And whisper they do, for he sets off on his walks at unlikely hours, and stops to examine the humblest flowers. He is seen on the beach, staring out across the waves as if he's searching for clues. But Mac isn't a detective, he's the architect Charles Rennie Mackintosh, and together with his red-haired artist wife, they soon become a source of fascination and wonder to Thomas.