The Case Is Closed

MRINAL SEN'S ''Case Is Closed'' begins by introducing a middle-class Calcutta couple who are flirting with the idea of hiring a young servant. Soon thereafter, a lower- class boy of about 11, not much older than their own son, enters the couple's employ. The film, which opens today at the Film Forum, is about the aftermath of an accident that occurs some months later. The servant dies, apparently of carbon monoxide poisoning, while sleeping in a windowless kitchen on an especially cold night. He was supposed to have slept in an unheated cubbyhole under a stairwell.