Claim: Lumen Pierce appears during a season.

Lumen Ann Pierce is a fictional character portrayed by Julia Stiles in the Showtime television series Dexter , season 5 . Lumen is introduced in the third episode -LRB- `` Practically Perfect '' -RRB- as a survivor of rapist-serial killer Boyd Fowler . She remains for the rest of the season , and leaves following the season 5 finale , `` The Big One '' .   In season 5 , episode 5 , `` First Blood '' , Lumen is revealed to have been beaten and gang raped by a group of men , including Boyd Fowler . She witnesses Dexter Morgan kill Fowler , and thus becomes a key player in Dexter 's life . Dexter rescues her , but initially thinks he has no choice but to kill her in order to eliminate a witness . He eventually decides to spare her life , however . To earn Lumen 's trust , Dexter shows her the fate of Boyd 's dead victims , tells her he saved her from the same fate , and confides his wife was murdered by someone like Boyd .   Lumen asks Dexter to help her seek revenge against her abusers , but he initially refuses . However , after Lumen continues on her own and targets the wrong suspect , Dexter teaches her the importance of knowing a person is guilty before killing him . He entreats her to leave Miami ; she agrees at first , but decides to stay after a pat-down at the airport brings back memories of her abuse . She goes out on her own and shoots one of her attackers , but panics not knowing what to do with his body ; she calls Dexter , who reluctantly helps her cover up the murder . That night , she tells him that killing the man brought her a sense of peace that she knows will not last ; she believes she will have to kill all of her attackers to get over her abuse for good . Dexter realizes that she harbors a `` Dark Passenger '' much like his and agrees to help , in part to find his own closure following Rita 's murder . The two then systematically hunt down and kill Lumen 's abusers , and in the process become lovers . Lumen leaves Dexter in the season finale , however , after realizing she no longer feels the need to kill .   Lumen exited the show following the events of `` The Big One '' .