Is there anything scarier than the inescapable final result of old age? As inevitable and gradual as it is, the onset of mortality and the accompanying shift in power that it creates still catches many parents and children by surprise and stretches already co-dependent households beyond their limits. Few if any among us can say that our lives have been directly touched by the tragedy of a machete-wielding maniac set loose at a summer camp, or by a cabal of Eastern European torturer profiteers luring nubile American tourists to their doom. An irrevocably sick parent’s slow demise and a child’s desperate inability to cope is a far more familiar — and no less horrific — story.

“The Living and the Dead,” an unusual new horror film opening today at the Pioneer Theater and playing through Halloween as part of the theater’s “Fourth Annual Month of Horror, Terror, and General Mayhem” series, compiles its modest body count among the ruins of an aristocratic English family that, even in the best of times, doesn’t appear to have had much chance at happiness. Lord Donald Brocklebank (Roger Lloyd-Pack), the family patriarch, struggles to keep body and soul together as his invalid wife Nancy’s (Kate Fahy) illness takes an increasing emotional and economic toll. The family manse, Longleigh House, has fallen into such disrepair that Donald must begin negotiations to sell off the rambling country estate before it crumbles to the ground.

Worse, the dwindling personal resources Donald must deploy each day to deal with his wife’s decline are stretched out along two different fronts. James, the heir to Lord and Lady Brocklebank, is himself more than a handful. Portrayed by Leo Bill in a series of noisy and needy eye-rolling spasms of childlike enthusiasm and priggish entitlement, James initially appears to be the result of a horrific experiment to genetically splice the contestants from the vintage Monty Python “upperclass twit of the year” sketch with the cartoon Tasmanian Devil. “But I like people!” James whines as he lurches for the front door to welcome an unannounced visitor. “Yes, but they don’t like you,” his father growls while blocking James’s path. It’s not immediately clear whom Donald is protecting from whom.

When Lord Brocklebank grudgingly packs for a trip to secure a new owner for Longleigh House and, he hopes, a new lease on his wife’s expensive medical upkeep, he misjudges the lengths to which mentally ill James is willing to go in pursuit of his father’s approval and his mother’s dependence. Behind the estate’s doors, James’s inept caregiving grows increasingly confrontational. When James abandons his own medication in order to double mom’s pill intake, his ministrations become potentially lethal.

Bookended by flash-forwards to Donald alone, unkempt, and paralyzed by painful memories of the recent past, it’s not difficult to guess the outcome of “The Living and the Dead.” What is consistently surprising about the film, however, is how sincerely pitched the performances are, given the increasing shrillness of the psychodrama that ensues. Much of the credit goes to Mr. Lloyd-Pack as Donald, who fearlessly creates a portrait of a man whose inner light has been snuffed out by loss. Ms. Fahy shows a remarkable commitment and range of feeling, given that she is on her back for two-thirds of her time on screen, and Mr. Bill’s oddly ingratiating turn as James redeems one of the most thoroughly unlikeable and thankless film roles in recent memory. But in essaying the peculiarly satisfying experience of “The Living and the Dead,” the party most clearly responsible is the writer and director, Simon Rumley. Despite an unfortunate tendency in the latter third of the film to jettison much of the anxiety he has carefully built with specious time-lapse and pixilation effects, Mr. Rumley demonstrates a remarkable gift for composing frames within frames and using Longleigh House’s decrepit rooms and abandoned halls to expose his characters’ increasingly aberrant psychology. Equal parts Grand Guignol in the hysterical mode of Robert Aldrich’s “What Ever Happened to Baby Jane?” (Mr. Rumley’s script even quotes from Aldrich’s “Kiss Me Deadly”) and confrontational psychological horror of the contemporary Asian grotesque variety practiced by Chan-Wook Park, “The Living and the Dead” delivers a genuinely personal case of the creeps that, unlike most contemporary horror-genre fare, will outlast the end credits and subway ride home.

Through October 31 (155 E. 3rd St., between avenues A and B, 212-591-0434).