A valuable painting leaves the train station in Galway in a guarded carriage. When the train arrives in Dublin, the painting is gone.

Suspicion immediately falls on Mr Kavanagh, the train's guard. Twins Deirdre and Tim know their father isn't the thief, and they're determined to find out who is.

Along with their friend Joe, they race against time to track down the painting … but as they close in on the thief they find themselves up against powerful enemies. Soon the children are battling not just to clear Mr Kavanagh's name – but for their very lives!