She told me things, too, rather abominable things, about the way in which she had got Halderschrodt into her power and was pressing him down.

Halderschrodt was de Mersch's banker-in-chief; his fall would mean de Mersch's, and so on.

The "so on" in this case meant a great deal more.

Halderschrodt, apparently, was the "somebody who was up to something" of the American paper--that is to say the allied firms that Halderschrodt represented.
I can't remember the details.

They were too huge and too unfamiliar, and I was too agitated by my own share in the humanity of it.