When Colin discovers his son is on a murder charge in France, he trails his boat, The Dragonfly, across the English channel to try and help him. There he meets his granddaughter for the first time, and to take care of her during the school holidays, they embark on a journey through the French canals, where they land big fish and uncover burning secrets. A quirky American woman travelling on her own boat catches Colin's eye and invokes his granddaughter's ire.But can Colin get his son off the hook?