Robert Eggers’ directorial debut, “The Witch,” opens with the subtitle “A New-England Folktale,” which is an apt promise. More fable than horror flick, the film is a sometimes spooky, sometimes silly tale that explores the way America in 1630 worked — running on fear, desperation and religious fervor. As a period piece, “The Witch” is an authentic and painstakingly realized rendering, but as a horror film, it lacks an essential tension that would inspire real fear and dread.

The story follows a family of English pilgrims, driven out of their community for an unspecified religious infraction by the father, William (Ralph Ineson). They settle at the edge of a wood, alone, with only each other to rely on: mother Katherine (Kate Dickie), teenage daughter Thomasin (Anya Taylor-Joy), younger son Caleb (Harvey Scrimshaw), mischievous toddlers Mercy (Ellie Grainger) and Jonas (Lucas Dawson), and little baby Sam. One day when Thomasin is playing with Sam, he disappears before her eyes, plunging the family into crisis, and mother Katherine into despondent, wrenching grief.

The baby’s disappearance is too much to bear for the family, who are struggling with their crops, the harsh isolation and menacing woods. Father William entangles his eldest children into an increasingly tenuous web of lies, as they cover for each other rather than face of the wrath of Katherine, who has become imminently suspicious of blossoming Thomasin. Mother accuses daughter of stealing, lying, bringing in the devil, aided by the suggestions of Mercy, who spends most of her days romping with Jonas and the wild ram, Black Phillip.

But it’s not just paranoia that sends them spiraling — there is an otherworldly, supernatural force of evil visiting horrors upon the family. Flashes of terrible things that could have become of baby Sam, visions of who or what might be lurking in the forest, and a mysterious disappearance and subsequent religious possession of Caleb all point to witchcraft and devilry.

Aesthetically, “The Witch” looks and sounds to be every inch the gothic, naturalistic horror film that it could be. The atmospheric score, by Mark Korven, skitters strings from an atonal groan to a shriek, while Jarin Blaschke’s cinematography relies on natural light and the wooded splendor to create arresting images.

Somehow, all of these well-executed elements don’t fit together. The tone of the performances varies wildly, from deathly serious to downright funny, though Taylor-Joy is consistently strong. In building tension, there are moments that are wasted. The film lags heavily in between dramatic scenes, and those just don’t deliver enough verve to sustain a necessary sense of moody dread.

Perhaps it just isn’t scary if you aren’t afraid of what “The Witch” thinks you should be. Ultimately, that’s feminine sexuality, vanity, independence — all of which are embodied in Thomasin’s pubescent transition, her liminal state between girl and woman. This topic is a fascinating one to explore in a horror film, particularly one that references the era of the Salem witch trials and the fear and persecution of women in a patriarchal society. But “The Witch” doesn’t commit to a point of view, or take a stand on what it’s trying to say. It presents the audience with random and scanty grotesque imagery but doesn’t connect the dots. With its impeccable craft but flaccid storytelling, “The Witch” feels like a missed opportunity.