Ireland, 1911. A valuable painting has been stolen, and nobody knows how. In a guarded carriage on the Galway to Dublin train, the painting was there on leaving Galway and gone on reaching Dublin. Suspicion falls on the train staff, including Brendan Kavanagh, the guard on the train.

With their father under suspicion, twins Deirdre and Tim Kavanagh, and their friend Joe, turn amateur detective to try to find out who the thief was, and how the crime was committed.

Combining their individual skills, the trio deduce that an audacious sleight of hand was used to carry out the theft. But when they try to unmask the thief and prevent the painting being smuggled out of the country, they come up against a powerful enemy. And as the story reaches its climax they realise that they’re battling not just to clear Mr Kavanagh’s name – but for their very lives.