‘Night Swim’ review: The backyard pool holds some secrets

As supernatural thrillers go, “Night Swim” is a quick dip — persuasively acted and quite effective in its first half, scattered and woozy in its second. The latest Blumhouse Productions release works from a premise we’ll call “haunted house adjacent.” The house is fine. But the backyard pool is in a mood.

The latest family to figure this out is the Wallers. They’ve moved a lot. Father Ray (Wyatt Russell), a promising major league third baseman, has gone through the usual trades, though in recent months he has been sidelined with symptoms of multiple sclerosis and attendant rehabilitation. The relocations have also involved Ray’s school administrator wife, Eve (Kerry Condon, the terrific Oscar nominee from “The Banshees of Inisherin”); their naturally gifted athlete daughter, Izzy (Amélie Hoeferle); and socially isolated younger brother Elliott (Gavin Warren), a boy living in the shadow of his high-achieving, somewhat ruthless sister.

The new house, somewhere in the Twin Cities, bodes well at first, but the evil pool starts dropping hints early and often. A mysterious battery-operated toy boat appears on the pool’s surface, puttering around on its own. Unseen or barely glimpsed creatures from the beyond — human, or formerly so — yank adults and children alike into the water. Elliott hears the sad, ghostly voice of a girl trapped behind one of the vents. She’s the one in the 1992-set prologue who sets up the narrative.

All this works for a while, partly because the Wallers are more realistically delineated in their tensions and anxieties than the typical supernatural thriller family unit. Condon’s the ringer, rendering every scene if not believable, then at least grounded. The idea in “Night Swim,” directed by second-time feature director Bryce McGuire from a script he wrote with Rod Blackhurst, hinges on the sinister underwater realm beneath the spring-fed pool itself.

At a key juncture in the second half, Eve pays a visit to one of the house’s previous owners. Jodi Long’s very good in the role, but this is where “Night Swim” starts dog-paddling in rivers of exposition, explanation and, for the audience, mild-to-moderate exasperation. Even so, I do like the duality of the pool’s nature: It’s a healing natural spring for some, a watery hellhole for others.

“Night Swim” comes from a crafty 2014 short directed by Blackhurst and McGuire, not quite three minutes in length minus end credits. Apples and oranges, I suppose, but the short gets more done in terms of atmosphere and rhythmic wiles than the full-length version. Still: These filmmakers have both a past and a future in evocative horror. The traditional pool game of Marco Polo has been waiting for its jump-scare showcase a long time now. (Did I miss an earlier thriller to exploit it?) And throughout “Night Swim,” the wonderfully uneasy musical score by Mark Korven (”The Witch”) evokes in ripples of sound what the film itself can’t always match with images.

“Night Swim” — 2.5 stars (out of 4)

MPA rating: PG-13 (for terror, some violent content and language)

Running time: 1:38

How to watch: Premieres in theaters Jan. 4

Michael Phillips is a Tribune critic.

mjphillips@chicagotribune.com

Twitter @phillipstribune