Winner of the Grand Jury Prize at the Sundance Film Festival, this haunting tale of twisted obsession also comes alarmingly close to being arty and soporific. For avoiding that abyss, director Jonathan Nossiter, who wrote the script with James Lasdun, owes a debt of thanks to David Suchet and Lisa Harrow, who give exceptional performances. Suchet, the star of TV's Poirot, plays Oliver, an out-of-shape IBM accountant who is also out of a job, a home and a wife, and reduced to living at a homeless…