When the National Gallery in London is flooded, the Director, Quentin Lester, decides to transfer the entire collection to the Welsh caves where the collection was stored during World War II. The entire operation is supposed to be secret and the cover story is that they are a mining company looking to reopen the mines, good news to the nearby economically-depressed town. It takes local school teacher Angharad Stanner all of a day to learn what is really going on, though. She soon has the entire school at the site taking a tour, but Quentin's refusal to open any of the packing crates leads to something of a falling-out. Gradually, Quentin gets to know the locals, particularly the Hughes family. In the end, everyone benefits and learns from one another.