Dublin in 1911 is an atmospheric city of cobbled streets, gas lamps and horse-drawn carriages. In a wealthy part of town, Isobel Forsyth, a feisty schoolgirl from a powerful family, is kidnapped by criminals. Kept prisoner in a remote farm on the Cooley Peninsula, Isobel is determined to fight back, and secretly sends out an SOS.

Fresh from being awarded police medals for their detective work on The Case of the Vanishing Painting, twins Tim and Deirdre, and their friend Joe are rewarded by a pre-Christmas visit to Aunt Helen’s farm, outside the village of Carlingford.

When the friends stumble across the crime, they’re excited to go on another adventure. But trying to rescue Isobel is more challenging than they expect, with hidden agendas and unexpected betrayals complicating their task. Unsure who they can trust, and with their own lives in danger, the children risk everything to save Isobel.