Cold Shoulder Road — Joan Aiken

Having freed the children enslaved in the northern mines, Is Twite and her cousin Arun return to Folkestone to find Arun's mother. But she has disappeared without a trace. There's plenty of evidence of strange goings-on now that the Channel Tunnel is open, and smugglers called the Merry Gentry have the whole countryside terrified. Have they abducted Arun's mother? Is and Arun are up against the evil Dominic de la Twite and the sneaky Admiral Fishskin in this fast-paced, wickedly witty adventure.