Behind the scenes

1. Things that are taking place or are located out of sight of the public at a theater or organization to ensure essential operations are maintained. Scene changeovers and lighting, prompters are examples.
2. Things that are secret or are often unknown, but yet essential for something to occur but may not be essential or useful to a formal group or a person's needs.
A couple having an affair but not married to each other may be conducting their trysts behind the scenes (of their marriages and spouses).