Of course, I was right. The second installment, "Black Coral," is now out, with no signs of a sophomore slump. Once again Mayne and his sleuths wade into the murky, python-infested waters of South Florida, where the plot runs much faster than the currents. Mayne's heroine is Sloan McPherson, a diver, sometime grad student in marine archaeology and, now, an officer with Florida's new state Underwater Investigative Unit. As our story opens, Sloan's doing a favor for the Highway Patrol, recovering a body from a pickup that ran off the road into Pond 65, in the outflow from a nuclear power plant.