What is the main conflict in Skin Tight by Carl Hiaasen?

The tranquil life led by Mick Stranahan on his stilt house in the tidal flats of Biscayne Bay is rudely shattered when a man, pretending to be his friend Tim Gavigan, drives up with a speedboat and attempts to shoot him. Mick Stranahan defends himself with a trophy Marlin's spike from the wall of his house and fatally stabs his assailant in the chest. Then, Stranahan, who is retired from being an investigator for the State Attorney Office, goes in search of the person or persons who are trying to get him killed.