Starring Kate Greenhouse and Aidan Devine. Rating unavailable. Opens Friday, November 11, at the Granville 7

What could be scarier than being diagnosed with a fast-growing, malignant brain tumour? Not much, I figure, and the makers of The Dark Hours would likely agree. That's why they made that most dreaded medical assessment a focus of their effective, unnerving little psychodrama.

Kate Greenhouse took the best-actress award at Montreal's prestigious Fantasia Film Festival for her role as Dr. Samantha Goodman, a 30-ish psychiatrist employed at an institution for violent sexual offenders. We learn early on, when she goads one of her patients during a parole review, that the doc can be cold and clinical. But she's got a lot on her mind-literally. Those foreboding CAT scans she's studying on company time aren't taken from a doomed inmate's file. That's her own diseased brain on display.

Hoping to break the news of her dire situation to her struggling-writer husband (Waydowntown's Gordon Currie), she meets him-and her untrustworthy younger sister (Iris Graham)-at the couple's remote cottage. The atmosphere is tense from the get-go, but the weekend turns particularly ugly when a harmless-looking young man (Flower and Garnet's Dov Tiefenbach) shows up at the door seeking shelter from the cold. Warming up by the fireplace, the skinny geek pulls a gun and holds the trio at bay until the arrival of his psychotic mentor, Harlan (Aidan Devine, one of Ed Harris's thugs in David Cronenberg's A History of Violence). The hulking Harlan is a former patient of Dr. Gordon's, and, seeking payback for his mistreatment at her hands, grabs an axe and forces everyone to play humiliating and/or painful games that reveal hidden desires and motivations.

The Dark Hours is similar to current body-count flick Saw II in that its main action revolves around a vengeful, intelligent sadist forcing helpless captives to jump through twisted hoops. But there is none of Saw II?'s lightning-fast edits or shreiking sound effects. Tailoring his feature debut to a more discerning genre crowd, director Paul Fox aims for a lower-key vibe of simmering dread, and-aided by Greenhouse's complex portrayal and E.C. Woodley's eerie score-quite often finds the mark. There are jolting moments of unbridled violence, but the real terror lies in imagining just what type of carnage the unhinged Harlan could unleash with that woodchopper of his. Not to mention that common pair of pliers.