Ethan Hawkeis capable of making terrible movies (“Maudie”), but only by accident. He doesn’t make cynical movies that were never intended to be any good, and so going into “The Black Phone,” we have the right to expect a serious attempt at a quality horror movie.

Well, an honest attempt is what we get. “The Black Phone” has better-than-average acting, an interesting period setting and well-developed characters. But it runs out of story less than halfway through, forcing the filmmakers to repeat the same kinds of actions, over and over, to stretch it to feature length.

The film takes place in 1978, for no obvious reasons besides that the first “Halloween” was released in 1978, and so something in that era’s look suggests horror. We meet 13-year-old Finney (Mason Thames), who is having trouble with bullies in school, and Finney’s younger sister, Gwen (Madeleine McGraw), who is pushy and fun and has clairvoyant gifts. The brother and sister are close, brought together by shared misery — their mother is dead, and their father (Jeremy Davies) is a drunken, abusive moron.

All this would seem a decent jumping-off point for any movie. So why bring in a serial killer and drag in the supernatural?

And yet, that’s how it is with the horror genre. It takes everything individual and specific, and funnels them into a fairly standard set of screams. The inevitable screaming this time derives from the pen ofJoe Hill, who comes by this line of work by inheritance. His birth name is Joseph King, as in the son of Stephen King.

So this middle school drama is going along interestingly, but then soon,folks notice that kids are going missing — probable victims of “the Grabber” (Ethan Hawke). The situation comes close to home when one of Finney’s best friends is grabbed, and even closer when the Grabber approaches Finney and asks if he wants to see a magic trick.

For the record: The proper answer to that question is always, “No.” But, of course, Finney wants to be polite, and so the next thing he knows, he’s stuffed into a van and drugged. When Finney wakes up, he’s in a soundproof basement, with nothing but a bed and a telephone that supposedly doesn’t work.

Here’s the problem with “The Black Phone” in a sentence: Once Finney is put into prison, so is the audience.

From that point on, he’s there and we know he can’t get out until the movie is over. That means that absolutely nothing that happens after Finney’s imprisonment can be of any consequence, at least not until 10 or 15 minutes before the finish.

Faced with a long empty stretch, director Scott Derrickson (“Doctor Strange”) and the screenwriters try to keep things lively, but there’s nothing to be done. They can’t scare us with what they might do to Finney, since nothing truly awful can happen until the end. Hawke makes his occasional basement visits, wearing a creepy mask, saying creepy things, but it’s still just two people talking in a basement.

The phone keeps ringing, and Finney keeps answering. The calls are from the Grabber’s dead victims, and they’re full of advice! But nothing can amount to anything until … well, you know. This is beyond dull; it’s sleep-inducing.

The movie comes close to springing to life only in the scenes involving Gwen, who prays for clairvoyant dreams that will help her locate her brother. McGraw is, by far, the best thing in “The Black Phone,” and if she can hold on to her feistiness through that self-image minefield known as puberty, I predict a successful adult career.

K“The Black Phone”:Horror. Starring Mason Thames, Madeleine McGraw and Ethan Hawke. Directed by Scott Derrickson. (R. 102 minutes.) In theaters Friday, June 24.