Horatio Entwhistle and his best friends-lock picker extraordinaire Ming, her cousin Grace, and gadget expert Wheels-have defeated many of Australia's dastardly villains using Horatio's patented Stupendous Glue. While on holiday at Nan and Pop's, they're literally struck by their newest adventure! Sailing toward Crystal Lake to camp for the night, Ming and Wheels are shocked when their boat is suddenly rammed by a large cruiser. The unfriendly man onboard accuses them of trespassing and warns them never to return. Horatio and Grace hurry to rescue their friends from the capsized boat. They make camp but wake to find their food, supplies, and glue stolen-and a No Trespassing sign posted. When Wheels uses his turbocharged wheelchair to explore the area, he overhears the angry stranger arguing with his workers about a sand mine near the lake. The four friends investigate, only to discover that the man, Mr. Jones, and his employees are dumping large, mysterious drums of liquid inside the mine. While the young sleuths are searching for clues, they're caught and ordered to stay away. They don't, of course, and are soon up to their necks in intrigue-and danger. is the unforgettable finale to the series.