What about H. H. Hughson?

The Lloyd's of London representative initially seems to be a minor
character, and yet he plays a prominent role throughout the story.
1. It he that meets Robie in the flower shop.
2. It's he that gives Robie the Client list and tells him where Mrs.
Stevens and her daughter will be (offering to arrange a meeting).
3. It's he that is present just about every time
Robie is with Mrs. Stevens.
4. Finally, it's he that dances the night away
with Francie in order to give Robie the freedom "to catch a thief" as
the story goes.

That's a lot of involvement, yet the character has pretty much been
ignored. I first thought about this while watching the end of the story
and thinking how strange it was that someone like Hughson would
willingly become part of the 'real' masquerade, pretending to be Robie.

There would not be much of a story if Mr. Hughson wasn't helpful.

Rich