By DEREK ELLEY
Two sisters who haven't seen each other for 15 years gradually rediscover common ground and a way of relating to each other in "I've Loved You So Long," a movie that is utterly engrossing despite being, on the surface, about very little. Toplined by Kristin Scott Thomas as the slightly frumpy older sister, this first feature by teacher-turned-scripter Philippe Claudel will need strong critical support to make much of a loving dent theatrically, but is a quality item for upscale French movie buffs. Pic goes out in Gaul mid-March.

First seen distractedly puffing on a cigarette as she waits for her younger sister Lea (Elsa Zylberstein) at an airport, Juliette (Scott Thomas) is a plainly dressed, middle-aged woman with tired hair and even more tired eyes, whose backstory slowly emerges throughout the picture. Lea, married to lexicographer Luc (Serge Hazanavicius), has a full life that includes raising two adopted Vietnamese daughters and looking after Luc's ailing father (Jean-Claude Arnaud).

Explaining "auntie" Juliette's sudden appearance, Lea tells her pushy elder daughter Lys (Lise Segur) that she's "been away for a long time, and in England" -- a convenient explanation for British thesp Scott Thomas' slight accent. In fact, as is revealed a half-hour in, Juliette has been in prison for 15 years for killing her 6-year-old son.

Film is basically about people rebuilding emotional ties to a point where they can start a new life together, and Juliette herself can find closure with her sister. Though Lea's own family life has been affected by Juliette's crime -- which left Lea with a fear of giving birth -- she takes a major chance by inviting her older sister to stay with her.

Claudel's script is built out of everyday, unmelodramatic events, succinctly dialogued and not nearly as downbeat as the movie sounds on paper: Juliette trying to find a job, Juliette taunted by a friend (Olivier Cruvellier) at a dinner party, Juliette befriended by Lea's colleague Michel (Laurent Grevill). But pic's hub is the relationship between the two sisters -- one who's been ground down by years of guilt, and another who's opened a door for her sister to walk through if the latter so chooses.

Scott Thomas is aces in the lead role, with flashes of mordant wit that prevent it from becoming a dreary study in self-pity. Zylberstein, a variable actress who's very dependent on her directors, is good here, but lacks Scott Thomas' quiet heft and can't quite handle Lea's occasional emotional outbursts. Still, the sisters' dramatic final talk works just fine.

Setting in Nancy, eastern France, in Claudel's home province of Alsace-Lorraine, allows the characters to develop naturally, unencumbered by the familiar sites of a city like Paris. Jerome Almeras' lensing is bright and well composed, and pacing is easy, making the almost two-hour running time pass smoothly.

Camera (color), Jerome Almeras; editor, Virginie Bruant; music, Jean-Louis Aubert; art director, Samuel Deshors; costume designer, Jacqueline Bouchard; sound (Dolby Digital/DTS Digital), Pierre Lenoir, Stephane Brunclair; assistant director, Julien Zidi. Reviewed at Berlin Film Festival (competing), Feb. 13, 2008. Running time: 117 MIN.