“Captain,” I said at last, “there is something deuced underhand about this brig. You tell me you've been to sea a good part of your life. You must have seen shady things done on ships, and heard of more. Well, what is this? is it insurance? is it piracy? what is it about? what can it be for?”
“Mr. Dodd,” returned Nares, “you're right about me having been to sea the bigger part of my life. And you're right again when you think I know a good many ways in which a dishonest captain mayn't be on the square, nor do exactly the right thing by his owners, and altogether be just a little too smart by ninety-nine and three-quarters. There's a good many ways, but not so many as you'd think; and not one that has any mortal thing to do with Trent. Trent and his whole racket has got to do with nothing—that's the bed-rock fact; there's no sense to it, and no use in it, and no story to it—it's a beastly dream. And don't you run away with that notion that landsmen take about ships.
I take "not one . . . has any mortal thing to do with Trent" to mean "has dead certain nothing to do with Trent" or ". . . next to nothing to do with Trent, right? I've found the following figurative meaning in the Collins dictionary: 12. conceivable; possible // of no mortal value to the owners