It's really a film about a woman in desperate need of a deprogrammer's snapping.
Their best guess is that Martha has fled a dodgy boyfriend, and she herself releases no further clues. Her conduct, however, hints at more than heartbreak. It is one thing to ask them, “Is it true married people don’t fuck?,” which might be no more than the provocative pose of youth; to climb into bed beside the married couple while they are making love—as Martha, schooled in group sex, naturally does—signals an insolence of another order. “That’s not normal, it’s private,” Lucy cries, and her verbal confusion pulls us toward the clever core of the movie. The easiest option, which would have produced a nifty horror flick but little else, would have been to build an ideal, love-warmed nest of the bourgeoisie and then, as in “Fatal Attraction,” have it invaded by shrieking demands from without. The effect of “Martha Marcy May Marlene,” on the other hand, is to peck away at what Lucy and Ted would claim as their well-earned happiness. Even the tiniest gestures on Martha’s part—opening a can of beer and tossing the ring-pull aside, or trying on a dress and dropping the hanger for Lucy to pick up—are invested with something more warped, or more scornful of our regular habits, than simple sloppiness. Ted never makes a definite move on Martha, but you can sense the squirm of desire within him, and when he solemnly informs her, “We are trying to have a baby,” her laugh—rich, robust, and mad—slaps him into a look of wounded panic. She already has a family, ready-made. She may have slipped its grasp for now, but not for good. When, at a low ebb, she calls the number of the farm, speaks briefly, then slams down the phone, somebody calls right back.
Check. It. Out.