Fireman Sam S05E12 - Deep Water

Norman Price is fascinated by Sam's Beep-o-matic, a high-tech metal-detector, in fact, he can't keep his hands off it. When Sam's back is turned, Norman and Mandy borrow the Beep-o-matic and go treasure hunting. But the children's over-zealous digging causes Mandy to tumble into a Celtic burial mound, and Norman is forced to run for help as the hole starts filling with water from the thunderstorm raging above.