It's as clear as that overcast sky and the highwater marks on the cave walls how this Saturday spelunking is going to end. Once Chad (aptly nicknamed ""Bumblefoot"") and his pals have gotten themselves stranded beside an inexorably rising underground lake, they suddenly become very resourceful -- discovering a new passage to the surface and, incidentally, an old station of the underground railroad (what else?). As a purely physical feat their escape commands attention; otherwise, the story values are rock bottom.