Thea's (Willa Holland) condition is deteriorating that even her estranged father, Malcolm (John Barrowman), fears for her life in the upcoming episode of The CW series "Arrow."

In "Sins of the Father," CarterMatt reports that Thea's thirst of blood continues to consume her weeks after her release from the Lazarus Pit. Her brother Oliver (Stephen Amell) is desperate to find a cure and relieve her of the pain she is feeling. Malcolm is also worried about Thea's situation and will decide to "step in" to help her. Perhaps, he should be more concerned about himself, as it appears Nyssa (guest star Katrina Law) is planning something against him.

The new Ra's al Ghul will return to Star City to offer Oliver something he will have difficulty refusing. Nyssa will tempt the green vigilante with the only means to save Thea. She will ask him to kill Malcolm in exchange for his sister's life. In the promo, Thea looks bad. Oliver is beside himself with worry. As the clip suggests, Oliver will take on Nyssa's offer, as he is shown locked in a fierce fight with Malcolm.

Elsewhere, Laurel (Katie Cassidy) will do her best to convince Nyssa to stop whatever it is she is planning. Her plea, however, may have no effect on the other woman. The teaser shows Nyssa arriving in the city with her band of followers. There is a good chance she had planned this all along so her ascent to power will be easier. Nyssa is using Oliver to kill the foe she has difficulty defeating.

Meanwhile, co-executive producer Wendy Mericle shared with TV Line new information regarding the villain known as the Calculator. He is indeed Felicity's (Emily Bett Rickards) father, Noah (Tom Amandes), who has come to the city after seeing his daughter in the news.

"Her father's re-appearance was really motivated by the midseason finale. The fact that she goes through what she goes through and has to deal with this disability and the wheelchair, we feel like that really put her back in the public eye and her father's radar," she said.

"Arrow" season 4 airs Wednesdays at 8 p.m. EST on The CW.