A relaxing camping trip starts badly when the unpleasant Mr van Jaarsveld refuses the four school friends permission to camp at his campsite. The Invincible Four – Ralph (aka Takkies) twin sister, Janet, Thulani (aka Mielies) and Stanley (aka Toothpick) spy an abandoned mine and decide to relocate their camp there. There they meet Karl and learn of a historic family feud and yet that is not the only mystery happening. Why is van Jaarsveld moving equipment from his farm buildings to the abandoned mine? The Four find themselves compelled to investigate, no matter what the danger.