Katie Cassidy, who exited the CW series Arrow after meeting her tragic fate in Season 4 as Laurel Lance, is returning as Laurel’s doppelgänger Black Siren. The character will re-appear in episodes #522 and #523, and continue as a series regular in Season 6. Here’s what Arrow executive producer Marc Guggenheim had to say about Cassidy rejoining the cast: “One of the things that most excites us about Arrow is that we go where the story takes us.