Glenn Dixon

Before Mike Nelson can investigate the disappearance of two geologists the sea washes one of them upon the beach, his body bearing marks apparently made by the suction valves of a giant octopus. When later the body of a young boy is found with the same mysterious marks, Mike is sure that the killer is a diabolically clever man who has somehow found a way to duplicate the mark of an octopus.

Mike Nelson rescues an unidentified girl from drowning. The Immigration Department suspects she's an illegal alien. Released in Mike's custody, the girl confesses she was towed into the country underwater in a sea sled operated by a ring of border-runners.

Slade finds himself in possession of a key that treasure seekers would kill to get back: the key to the Seven Emeralds of Quetzalcoatl.