On one level, this very well done movie might be compared to "A Nightmare on Elm Street." City denizen "Mavis" contacts her old friend "Monique," who lives in a semi-rural enclave upstate. Mavis requests that Mo travel to her apartment for undisclosed, but serious, reasons.
When Mo arrives at the apartment, she learns that Mavis has been plagued by bad dreams that are increasingly violent and threaten to literally erase her, as if she had never existed. Key to these dreams, we learn, is a dark figure that controls the direction of the dream-narrative, as it were. Mo tries to help. But in so doing, she falls prey to the very dream "disease" that Mavis fell prey to. Much of the movie's balance, then, is concerned with Mo's dream world and her ideations.
On the other hand, the deep structure of the film is actually close to something like "It's a Wonderful Life" (or, heck, "Wild Strawberries"). The questions at the heart of it all: What if I depart now? What if I had never been? Erasure. We learn that these questions were already pertinent to Monique's life prior to her own "infection" by these disturbing dreams. But these questions also inform the general direction of a film that uses the isolation, impersonality and fear of the COVID 19 crisis as its backdrop and sensibility. In short, The Harbinger has ambitions beyond "the creepy."
To the extent the film meets these ambitions, Gabby Beans (Monique) deserves a lot of credit for carrying the central role from stern to bow. She is excellent. (Frankly, each of the actors was, at worst, very good.)
Mitton's writing also deserves a lot of credit. There are a few slow moments in the middle of the film. But in general, the Harbinger features tight, economical dialogue between the actors. And while the script owes more than one debt to its predecessors, it also avoids most of the expected horror movie cliches for a film in this genre (dream horror?), while playing on some familiar tropes (key among them, the "is the character imagining this, or is she really experiencing it" plot device).
Anyway, definitely recommended. Oh, and the closing scene was very well done in my opinion. A fine closer right up there with "Kingdom of the Spiders" or "Hereditary."
