Book review - "Grave Descend" by John Lange/Michael Crichton (warning: spoilers)

This Lange novel is about a diver in Jamaica who is hired to do an urgent mystery dive by some shady characters. You can feel the movie watching habits of Crichton through this - the hero feels like Robert Mitchum, the baddy like Sydney Greenstreet, the secret is a stashes of diamonds for the war.Crichton was an enthusiastic diver though so this has the benefit of some of his research and expertise on that. Only the diving really. The first half of this was stronger when the hero didn't know what was going on - once he does it's less fun. The women are hot and sexy, there's a loyal black who rescues the hero a lot in the second half which feels like cheating.