Dana Adam Shapiro (Murderball) does a decent job on this entry into the canon of movies about voyeurism. Too decent, perhaps — it could use more edge in dealing with the topic, as well as with the title subject. Brooklyn photographer Theo (Chris Messina) doesn't like his day job taking wedding pictures, and neither is he satisfied with his fiancée, Nat (Rashida Jones), who keeps finding excuses to avoid having sex with him. He seeks relief with his sideline service "Gumshoot," in which he stalks clients and snaps candid photos of them. Then "Subgirl," a mysterious beauty in a blond wig, hires him and his life starts to crumble. In their first session, she masturbates on a park bench, and things get kinkier after that. When Nat enters the hospital with a staph infection, Theo's obsession grows, but despite the pseudo-vérité style, the convincing improvised dialogue, and its intimations of Blow-Up and The Conversation, Monogamy never quite makes a full commitment.