不要把句子断章取义，应该是这样：

"Exactly. I have no doubt that you and I could carry it so far. Halloa, Watson, what's this? It's the man himself, by all that's wonderful and audacious! Not a word to show yow suspicions -not a word, or my plans crumble to the ground."

1. It's the man himself：主系表 + 同位语结构。

2. by all that's wonderful and audacious：修饰all 的定语从句。

3. by：指人的品质个性“由......表现出来”。by...短语作 the man 的非限制性定语。

这句话的含义是：他本人就是这样的一个人，令人赞叹和敢于冒险。