Apartment is a thriller mystery drama. The movie revolves around Preeti Sengupta (Tanushree Dutta), an air hostess, who lives in a rented apartment with her boyfriend Karan Malhotra (Rohit Roy). Preeti suspects that Karan is cheating on her and throws her out of the apartment. She then advertises for a tenant to share the rent. She is a simple, small-town girl Neha (Neetu Chandra), who becomes her roommate. Initially, everything goes right, and the two girls become friends in no time. However, soon Preeti experiences a series of mysterious incidents, causing her to rethink her decision of having a roommate.