Producers: John Schoenfelder, Russell Ackerman, Tomas “Dutch” Deckaj, Alex Mace, Matthew Baker and Isaac Clements   Director: Simon Barrett   Screenplay: Simon Barrett   Cast: Suki Waterhouse, Ella Rae Smith, Madisen Beaty, Inanna Sarkis, Seamus Patterson, Stephanie Sy, Djouliet Amara, Jade Michael, Megan Best and Marina Stephenson Kerr   Distributor: RLJE Films/Shudder       

Grade: C

Simon Barrett has written a number of horror scripts for director Adam Wingard, including the inexplicably well-received “You’re Next” (2010) and the genuinely clever “The Guest” (2014).  Now he takes to the director’s chair himself with his screenplay for “Séance,” an old-fashioned slasher movie with some supposedly supernatural undertones and a sadly ludicrous “surprise” ending.

The movie begins with a tragedy at the exclusive Eveldine Academy for girls run sternly by Headmistress Landry (Marina Stephenson Kerr).  A clique led by snooty mean girl Alice (Inanna Sarkis) plays a nasty joke on Kerrie (Megan Best), scaring her with a ritual involving a student who reputedly killed herself some years previously.  Kerrie rushes back to her room and falls from a window to her death, an apparent suicide herself.

Almost immediately a new girl arrives on campus, Camille (Suki Waterhouse), taking Kerrie’s now-vacant room.  (Though the place is said to be short of space, it looks absurdly empty.)  She’s befriended by nervous Helina (Ella Rae Smith), but quicly falls afoul of Alice and her band of followers, Bethany (Madisen Beaty), Yvonne (Stephanie Sy), Rosalind (Djouliet Amara) and Lenora (Jade Michael).  Her room also has oddities—flickering lights, strange shadows, noises—that lead her to call on the help of the campus handyman, Landry’s shy son Trevor (Seamus Patterson).

That prompts the girls to hold the titular ritual, which begins a series of additional deaths.  Yvonne gets stabbed while practicing a dance routine, and Lenora while walking outside; Rosalind is attacked in the shower.  Alice and Bethany focus their suspicions on Camille, though Helina remains steadfast in her friendship.  (In fact, there’s a hint of incipient same-sex attraction that, however, gets no traction.)  Eventually the truth about the masked killer’s identity is revealed, and the motives behind the killings are so ridiculous that even devotees of the genre are likely to find them unintentionally hilarious.  The revelations do, however, allow for some cat-fights and a pretty gory finish, even if the effects are fairly primitive.

“Séance” would benefit from a better script and more assured direction, but also from more compelling performances.  Besides looking too old for the role, Waterhouse is wooden and poker-faced, and Sarkis takes her caricature of the nasty prima donna too far; the young cast members are okay if unremarkable, at least until those who turn out to be bad in the last reel have to put on villainous airs.  Kerr does a Mrs. Danvers impression as the rigid headmistress.

But the picture does have a glossy visual sheen.  Mars Feehery’s burnished production design is shot lushly by cinematographer Karin Hussain, who also uses the snowy weather to some effect.  But the editing by James Vandewater is slack, though Barrett’s penchant for slow pacing dictates that to some degree, and the score by Sicker Man can’t amp up the hoped-for suspense.

“Séance” is a pro-forma masked slasher movie that doesn’t offer enough new narrative or visual twists to lift it from mediocrity.