Spurred by a Celtic Exhibition, Dee and Trevor go Treasure Hunting with Trevor's granddad's Metal Detector and guidance at Willowtree Farm. They find a cache of coins - that vanish by the time the Finds Liaison Officer attends. The farmer is suspected but there's no evidence. Dee and Trevor investigate. The Police get involved and follow Dee's idea of a 'Sting' but move too quickly letting the farmer get away with the evidence. More treasure hunting at Grainger's farm next door see Dee, Trevor and 6 yrs. old Nellie Grainger trapped in flooding cave. Escaping through a nuclear bunker just in time the do more treasure hunt, making finds of Celtic jewellery. The police raid Willowtree Farm but the farmer and his son escape. They crash into a parked police car, are trapped unconscious and the vehicle catches fire. Dee and Trevor try to pull them free but it takes Dee's stronger Dad to succeed. They find the stolen coins in the car.