Are you up for a thrilling adventure? When twelve year old Joe and his two younger sisters are invited by their friend Will to go camping in Wales, it doesn't take them long to stumble across a long-lost tunnel that leads to a valley full of secrets and surprises. Follow the children as they are imprisoned in an old farmhouse, discover a hidden cave, sabotage a plane, rescue a missing man, undertake a perilous climb, and more Book 3 in The Mystery Series, this adventure novel is set in 1950's Britain and will suit people who enjoy Nancy Drew, the Hardy Boys or the Famous Five.