Unable to sleep, 11-year-old Tom sneaks out of his house and heads down to the river that runs through the cliffs near his home. Here, he climbs onto a large piece of packing foam (leftover from the new refrigerator that was delivered earlier that day) and embarks on what he believes will be nothing more than a leisurely float down the river. Little does Tom suspect, he is about to go on the ride of his life! The foam raft sweeps Tom down the river and deposits him into a series of underground caves rumored to hold buried treasure. Here, in the depths of the earth, Tom encounters a stray dog with a knack for disappearing, a long-trapped explorer, ancient artifacts, and deadly secrets that will change his life forever.