Lumen Pierce appears on the TV show Dexter.
Lumen Ann Pierce is a fictional character portrayed by Julia Stiles in the Showtime television series Dexter , season 5 . 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 . 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 . `` The Big One '' is the fifth season finale of the American television drama series Dexter , and the 60th overall episode of the show .