Dublin, 1912.The long summer stretches out before twins Tim and Deirdre. Their friend Joe is over a hundred miles away in Limerick ... but when Deirdre spots a boy who looks exactly like him on a Dublin beach, the twins realise they have a puzzle on their hands!As they begin to uncover the facts about Joe's double, they realise there's a big family secret to be revealed.Can the friends solve their biggest mystery so far?