Documentary filmmaker Doug Block was still mourning the death of his beloved mother when his father, a relatively remote figure, startled him and his sister by marrying the woman who’d been his secretary 40 years earlier. After learning that his parents’ 54-year marriage hadn’t been nearly as happy as he’d assumed, Block started reading his mother’s voluminous diaries, and this film charts his discoveries during that period, when his father was packing up his belongings and preparing to move from Long Island to Florida with his new wife. This isn’t always adept as storytelling, and Block’s coming to terms with his own denseness occasionally tries one’s patience, but he manages to make the overall process of his reeducation fascinating and compelling. 90 min. (JR)