"Man overboard! Ten dollars if you'll carry me to the mainland!" And now he could see against the paler hue of the sky.

the dark outlines of the boat's prow.

It was bearing down on him.
Above the bow's edge he could make out the vague silhouette of a head and upper body.
Then into his memory flashed something which the shock of his upsetting had completely banished.

He recalled the motorboat which had darted, arrow-like, out from around the southern edge of the mangrove swamp, and which he had been watching when his scow went to pieces on the reef.
If this were the same boat--if its steersman chanced to be Milo Standish crossing to the key to learn if his murderplot had yet culminated--so much the better! Man to man, there between sea and sky in the gathering gloom, they could settle the account once and for all.
Perhaps Standish had recognized him.

Perhaps he merely took him for some capsized fisherman.