The accidental death of a boy and the kidnapping of another, while stunning plot turns, are portals into even more fascinating psychological territory in Alias Betty, a nifty, entwined, ultimately gripping adaptation of British crime writer Ruth Rendell's novel ''The Tree of Hands'' by French director Claude Miller (''The Little Thief''). The dead child was the son of Betty Fisher (Sandrine Kiberlain), a successful novelist living in the suburbs of Paris. The kidnapped child is the ''gift'' of Betty's mad and maddeningly unmaternal mother, Margot (Nicole Garcia). Everybody's awful and flawed in this anti– fairy tale (including the stolen boy's slutty mother, who's just as happy her kid is out of her hair). But everything is right about the merciless performances of Kiberlain and Garcia, and about the way Miller layers the stories of these weaklings, tugging at the ties, however warped, that bind parent and child.