Beware of movies that are all glancing, naturalistic atmosphere — they can end up hitting you over the head with their ominous yet vague serenity. Credit director Christine Jeffs for this, though: She knows how to stage a boozy, snog-your-neighbor party in a seaside New Zealand cottage in 1972 so that it feels like 1972. (”Spooky” is on the turntable, and the dancing looks like a slow form of passing out.) The party host, Kate (Sarah Peirse), is a voluptuous, depressed wife and mother who, as the summer progresses, carries on two affairs: one with whiskey and lemon, the other with a handsome photographer (Marton Csokas) who has also caught the eye of her 13-year-old daughter, Janey (Alicia Fulford-Wierzbicki). The movie is Janey’s tale, and as it moves from the drizzly to the overly stormy, Rain freights a young girl’s self-destructive eagerness to lose her virginity with so much danger and even horror that it’s as if the events were trying to make up for the film’s previous lack of drama.