‘Them’ taps another vein of horror in the Black experience of the 1950s 

“This is how it begins. How it changes. With one family,” she says.

As for that family, the dad, Henry Emory (Ashley Thomas), has a good job as an engineer, but one that requires swallowing a steady diet of racism from his condescending boss. Henry’s wife, Lucky (Deborah Ayorinde), brings a terrible past with her from North Carolina, a grim interlude that will eventually be revealed in gruesome (too gruesome, possibly, for some) detail, explaining the impetus behind the move west.

Nor are their young daughters, impressively played by Shahadi Wright Joseph and Emily Hurd, spared the ordeal as the episodes progress, mixing supernatural flourishes with more mundane horrors.

“Them” maintains a sense of dread with eerie music and disturbing images, but the macabre component to what’s happening coexists somewhat awkwardly with issues surrounding segregation, corruption and financial exploitation.

Juggling that stew of material, the series manages to be bracing and uncomfortable and still feel uneven. That’s a byproduct, perhaps, of employing the limited-series format as opposed to a movie, as the individual episodes move briskly enough (several run less than 40 minutes), but the overall story feels stretched out in the middle, then rushed at the end.

The central cast is extremely good, and there are plenty of nifty period beats, like Henry buying a black-and-white TV and sitting down to watch “Father Knows Best,” the perfect symbol of carefree ’50s suburbia.

“Them” carves out its own place in that continuum, presenting an unflinching view of hatred and fear, with violence as a brutal consequence. Yet the net effect underscores the challenge of wedding sobering reality and horror conventions, in a way that’s intriguing but less than fully satisfying.

“Them” premieres April 9 on Amazon.