After the high-profile Oscar bait of The Others and Moulin Rouge, Nicole Kidman gets to slum a bit and strut in her birthday suit in Jez Butterworth’s low-budget, low-ambition British romantic comedy. She’s more the gift than the celebrant as "Nadia," the love bunny ordered up by moony loser John Buckingham (Ben Chaplin) from the "From Russia With Love Agency" to share his ant-infested bungalow in hideous St. Albans. John works as a teller in a bank where the HR department engages employees in a game called "Trust and Letting Go." But Nadia quickly determines that good-old-fashioned bondage and discipline is more to John’s taste, and it’s all fun and games until her friends Yuri (Vincent Cassel) and Alexei (Mathieu Kassovitz) show up and you have to ask yourself how many movies would last longer than 20 minutes if the characters called in the authorities at the proper time. In the subsequent shenanigans, Kidman is kittenish, Chaplin is downcast, and Kassovitz has the brute charm of a vicious ruminant. Birthday Girl might have been more of a treat had Butterworth trusted to his darker inclinations and let go of the feel-good wrappings.