Read it through once

"Wilson, you're not a fool--a fact of recent discovery. Whatever your scheme was, it had sense in it, Blake's opinion to the contrary notwithstanding. I don't ask you to reveal it, but I will suppose a case--a case which will answer as a starting-point for the real thing I am going to come at, and that's all I want. You offered five hundred dollars for the knife, and five hundred for the thief. We will suppose, for argument's sake, that the first reward is advertised and the second offered by private letter to pawnbrokers and--"