sub-rosa
under-the-table
behind-the-scenes

He knows how to work behind the scenes to get things done.

People were working hard on the problem behind the scenes.

But behind the scenes they don't like each other very much.

The others had to work behind the scenes at the show.

Political forces are at work behind the scenes as well.

All the others will be working for the American team behind the scenes.

After three years of working behind the scenes, nothing changed so I went public.

Or perhaps he was simply the man behind the scenes?

People who have spent time with him behind the scenes say the picture is not much different in private.

Much, however, already had and was to happen behind the scenes.