Upon what did the success of Percy’s plan depend?

Percy's plan depended upon the fact that in dressed like a Jew, the Frenchmen wouldn't come any closer to him than they had to.

I know human nature pretty well by now," he added, with a note of sadness in his cheery, young voice, "and I know these Frenchmen out and out. They so loathe a Jew, that they never come nearer than a couple of yards of him, and begad! I fancy that I contrived to make myself look about as loathsome an object as it is possible to conceive."