A family unit is like a fragile ecosystem—the introduction of a foreign species can have dangerous ripple effects. In Ry Russo-Young’s Nobody Walks (co-written by Girls’ Lena Dunham), sexy gamine Martine (Olivia Thirlby) stays for a brief spell in the pool house of an L.A. clan, and changes everyone, for better and for worse. The film takes place over the course of a few hot, summery weeks during which Martine enlists sound engineer Peter (John Krasinski) to help her with a short art film she’s making. Peter’s wife, Julie (Rosemarie DeWitt), is both welcoming and wary of their houseguest. Julie’s daughter, Kolt (India Ennenga), is fascinated by Martine, and watches her every move through the airy home where most of the film’s action takes place. Martine’s a magnetic figure who’s apparently irresistible to nearly every dude she comes in contact with, and Russo-Young deftly handles the sexual tension between she and Peter (and Peter’s foxy assistant). The film is thoughtful and low-key, but as the action revs up, it packs a wallop; Thirlby’s performance is brilliantly understated, and Krasinski and DeWitt are extremely convincing as a married couple in a moment of crisis. Nobody Walks is reminiscent of Laurel Canyon and Swimming Pool, both of which focus on compelling women in the midst of sweaty, sensual summers that alter their lives forever. Ultimately, it’s a meditation on the power of female sexuality, and the ways in which it can manipulate, confuse, inspire, and destroy.