When Lily moves into new boyfriend Marcus's apartment and plunges headlong into their relationship, she must contend with an intangible, hostile presence—Marcus's ex-girlfriend, Sinead. As Lily and Marcus become more deeply involved, Lily becomes obsessed with Sinead's fate and thinks she sees her everywhere. She must question not only her sanity, but whether the man she loves is someone she can, or should, be with at all.