It is 1914, and Thomas Maggs lives with his parents on the Suffolk coast. Life is quiet, shaped by the seasons. Then one day a mysterious Scotsman arrives, looking for all the world like Sherlock Holmes. Mac is what the locals call him as they whisper. But Mac isn't a detective; he's the architect Charles Rennie Mackintosh, and together with his red-haired artist wife, he soon becomes a source of fascination and wonder to Thomas.