The Deep Blue Goodbye: John D. MacDonald

Travis McGee is a big tough beach-walker, a knight-errant and salvage expert, prepared to risk life and limb to recover stolen goods - provided he gets half. He can't resist the challenge of helping Cathy Kerr, a desolate young dancer defrauded of the treasure her father had amassed during the war. They don't know what the treasure is but they knew who stole it - Junior Allen, a smiling man who had met Cathy's father in prison. He took up with Cathy long enough to destroy her soul and find the hiding place. It's easy to find Allen's trail - by the money he flaunts the women he's depraved.