"Arrow" season 3, episode 4 spoilers hint that Oliver might break his vow against killing ever again, as Sara's death triggers his quest for justice.

The promo video showed "Arrow" season 3, episode 4 spoilers as Oliver Queen will have to make a choice when Ra's al Ghul is about to descend on Starling City.

"I understand you're not killing people these days," John Barrowman tells Oliver Queen. "Break your vows, kill your sister's father."

In the last episode, Oliver hit a dead end in the investigation into Sara's death. So instead, he redirected all his attention into helping his sister who was training in Corto Maltese, where Felicity managed to trace her, with Malcolm Merlyn.

Oliver Queen managed to convince her into going home to Starling City after revealing to her the truth about their father's death. But Malcolm Merlyn was not about to let her go so easily and so went back to Starling City to get her back.

The synopsis from Comic Book revealed quite a lot of "Arrow" season 3, episode 4 spoilers as it reads:

"In the "The Magician" episode of Arrow, A furious Nyssa (guest star Katrina Law) confronts Oliver (Stephen Amell) about Sara. When Oliver learns Malcolm Merlyn (John Barrowman) is alive, he suspects Merlyn killed Sara. Oliver and Nyssa join forces and go after the Dark Archer, intent on bringing Sara's killer to justice. Laurel (Katie Cassidy) keeps her distance from Nyssa, as she blames her sister's death on her involvement with the League of Assassins. Meanwhile, Oliver and Roy (Colton Haynes) work on repairing their respective relationships with Thea (Willa Holland), who has returned home. Nyssa discusses Oliver with her father, Ra's al Ghul (guest star Matt Nable)."

"The Magician" is written by Wendy Mericle and Marc Guggenheim. Directed by John Behring, the episode will air on October 29 at 8 p.m.