A woman who studies butterflies and moths tests the limits of her relationship with her lover in Peter Strickland's third feature film, following Katalin Varga and Berberian Sound Studio. Evelyn works hard to match Cynthia's academic skills, but she also has increasingly demanding desires and needs of her own. Day after day the couple act out a simple ritual that ends in Evelyn's punishment, but Cynthia yearns for a more conventional relationship. Evelyn's obsession quickly becomes an addiction that pushes their relationship to breaking point.