I think I saw this black and white movie in the 40’s or 50’s. A man gets locked in a big store overnight and discovers that there are other “night people” living there. They become like models if a night watchman comes. He finally is accepted into their company but finds he can’t leave or the mortuary people will come for him and turn him into a model. But he falls in love with one of the youngest and tries to escape. I don’t think he made it.