This week The CW has femme fatales from the past who return and wreak havoc on Arrow and Supernatural; a Salvatore brother revisiting his past in New York City circa 1970 on The Vampire Diaries; Vince and Cat leaving the past behind and starting their relationship anew; and on Cult, Jeff and Skye dress up for a “Cult” fan costume party, but find they may be in over their heads.