The Lone Pine Club comprises David Morton, Richard ("Dickie") Morton and Mary Morton (twins), Petronella ("Peter") Sterling, Tom Ingles and Jenny Harman and in this tale they are searching for Roman relics in the countryside around Greystone Dingle, which is near the homes of some of the Lone Pine members at Barton Beach.
The story begins when Tom buys Jenny an old silver spoon at an auction. When the auction is over an old man asks Jenny if he can purchase the spoon from her but as she was given it as a present, and she also liked it very much, she was not prepared to part with it.
The old man, whose name turned out to be Mr Wilkins, persists but with no success. So he decides to tell Jenny and Tom that he feels there are Roman relics in the hills around Greystone Dingle and that the spoon could well be one of the artefacts that were buried there. As a consequence Jenny and Tom enlist the club members to go searching for treasure.
Meanwhile Mr Wilkins is taken away by a nasty family called Smithson and the five come across them in their caravan while on their way to the search area. It seems that the Smithsons are up to no good and when Dickie queries what is happening to Mr Wilkins Jenny answers, 'It's funny how we get mixed up with crime,' which they always seem to do in any of their adventures.
This story follows the same pattern and various encounters with the Smithsons end up with trauma for the gang and then when they reach Greystone Dingle they get caught in a tremendous rainstorm, so much so that they take shelter in a cave, which is one of their headquarters. Disaster strikes while they are there and three of the party need rescuing from a raging underground river that they discover and fall into.
They also continue to search for Roman relics and when a mosaic floor is uncovered by the raging torrent, they realise that they are in the right area. More nastiness occurs with the Smithsons and their son, who none of the five take a liking to, before Mr Wilkins and the others discover that they were correct in thinking that there were treasures buried in the area.
Everything eventually turns out for the best and Mr Wilkins joins the club members and their families in a celebration of the event as they plan what to do with their finds.
The story is a pleasant one and, while not all blood and guts, does keep the reader interested with the action that does take place ... and at the conclusion, the Lone Pine Five are forewarned by two occasional members of the Lone Pine Club, Jonathan and Penelope ("Penny") that they will soon be needed to investigate another mystery ...