S1, E4: "Frank outlines his larger plan for Cassie to go undercover as Lexie in order to find her double's murderer. Cassie turns him down flat. Meanwhile, the Katy investigation grinds to a halt, and Rob focuses his increasingly disturbed mind on tracking down Jonathon's two best friends from the past because he is convinced they hold the answers to both cases. As the pair are overwhelmed with memories of their traumatic childhoods, Rob and Cassie turn to one another for comfort and reassurance. But Rob cannot deal with any intimacy, and he is absolutely savage in his rejection of her. Reeling and feeling betrayed, Cassie agrees to Frank's plan to go undercover and play the role of the murdered young woman."