Actor Colton Haynes returns as DC Comics' Arsenal in The CW's 'Arrow' Season 4
Actor Colton Haynes arrives at the 20th annual Elton John AIDS Foundation Academy Awards Viewing Party in West Hollywood, California February 26, 2012. Reuters/Gus Ruelas

"Arrow" Season 4, Episode 12 airs this Wednesday on The CW. This week's new episode is called "Unchained." Nyssa (Katrina Law) and Arsenal aka Roy Harper (Colton Haynes) are moving their storylines forward, according to the show's official synopsis. It seems Roy would have more screen time this week, while Nyssa's presence would be stronger in the next episode.

Spoiler alert: This update contains "Arrow" Season 4 spoilers. Read on at your own risk if you're not caught up on the latest developments in the DC Comics-inspired series.

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"The team faces off against a formidable villain nicknamed The Calculator (guest star Tom Amandes). Meanwhile, Nyssa (guest star Katrina Law) makes her move and Roy Harper (guest star Colton Haynes) returns to Star City. Kevin Fair directed the episode written by Speed Weed and Beth Schwartz," reads the Arrow 4x12 synposis from The CW.

From the Arrow 4x12 promo video, it seems this villain is a computer whiz like Felicity Smoak (Emily Bett Rickards). Watch the promo video below. Haynes has said in an interview that his return as Arsenal gets sad toward the end if "Arrow" Season 4, Episode 12.

“It's really exciting, it's also really sad towards the end. Something really sad happens,” Haynes told IGN, adding that there will be some change in the dynamics of Team Arrow. He did not elaborate on what is "sad," but said he might return to at least one more "Arrow" Season 4 episode before it wraps up.

Is Damien Darhk Felicity's father? Damien Darhk (Neal McDonough) remains the most formidable enemy in "Arrow" Season 4. His wife, Ruve (Janet Kidder), could be just as evil. They are Oliver Queen's (Stephen Amell) biggest target this season. Incidentally, a show boss at "Arrow" has denied that Darhk is Felicity's father, but executive producer Wendy Mericle told Felicity's father is also a villain. TV Guide raises the possibility that this week's villain, The Calculator, is Felicity Smoak's father.

According to a separate "Arrow" Season 4 synopsis, Nyssa and Laurel (Katie Cassidy) would be having a heart-to-heart discussion. Fans are guessing it could be about Laurel's sister Sara, who is now time travelling in the spinoff series "Legends of Tomorrow" with Rip Hunter (Arthur Darvill). Could this episode be about Nyssa's quest to reunite with Sara? Perhaps they would be talking about other things, too. In the same TV Guide report, Law seems to hint that she would first have to deal with Malcolm Merlyn (John Barrowman), who is the new Ra's al Ghul. The "move" in the "Unchained" synopsis is linked to her quest for vengeance. After getting thrown in a dungeon, Nyssa is now unchained, unleashing her warrior self again.

Actress Katrina Law is in 'Arrow' Season 4 Episode 12 as Nyssa, unchained
Actress Katrina Law poses at a cocktail party hosted by Vanity Fair and Spike TV to celebrate Spike's new event series “Tut,” at Chateau Marmont in West Hollywood, California, July 8, 2015. Reuters/Danny Moloshok
WATCH: 'Arrow' Season 4, Episode 12 - 'Unchained' - The CW on YouTube

Source: The CW/YouTube/Promos and Previews