Frank and Joe Hardy are heading out on a caving expedition in Kentucky. But something's not quite right, and this particular decent reeks of danger. The boys are determined to get to the bottom of it, but their curiosity could prove fatal as they explore just that little bit too far. From unearthing a fellow caver with murderous intentions, to a life threatening dip in a vicious whirlpool, the brothers lurch from one near-death experience to the next. But can they uncover the truth before the dark, subterranean chamber traps them both for ever?