For a horror movie derived from a concept as singularly contemporary as an internet myth, A24’s Backrooms is grounded in a mourning for lost things that could only be called conservative.Like its foundational web-based myth — which, as far as I can tell from my position as one relatively estranged from internet subcultures, refers to the existence of a bewilderingly complex series of seemingly unused rooms adjacent to retail establishments — Backrooms summons fears of hidden places where few legitimate exits present themselves. Scary stuff, no?To his credit, though, director Kane Parsons — elaborating on his own YouTube series of the same title — has enlarged his film’s emotional palette. He means not just to induce fright but to encourage lament: for the early 1990s, when the new movie is set; for decaying strip malls and dying furniture stores, to which the backrooms here are affixed; and for the passing away of all structures, however cheap or shoddy, that hold meaning for us.

Chiwetel Ejiofor in “Backrooms.” (A24 Studios)

In the latter category is the childhood home of Mary (Renate Reinsve), a psychiatrist who confidently expounds her therapeutic philosophy in her sessions with clients and on late-night TV commercials promoting her self-help audio cassette tapes. That Mary herself, enveloped in her generously proportioned sofa and sitting before a literal TV tray with an actual TV dinner on top of it, watches one of her own commercials is a sign that her emotional wellness may be in doubt.