There’s just one episode left until the CW’s “Arrow” crosses over for the second time with “The Flash.” With the team closing in on Season 4's new and mystical enemy, they're whipping out the big guns and revealing a shocking secret that could change the dynamic of the Star City vigilantes forever. 

During last week’s episode, Team Arrow dealt a big blow to the villain Damien Darhk (Neal McDonough) when they launched a daring rescue of his prisoner, Ray Palmer (Brandon Routh). While the mission was successful, The Green Arrow (Stephen Amell) discovered that he’s going to be no match for his opponent's magical powers, ruling out another frontal assault attempt.

Meanwhile, his sister Thea (Willa Holland) has been struggling to keep the side effects she’s feeling from the Lazarus Pit under control. In Season 3, Thea was on the brink of death when her brother dipped her into the magical waters and healed her. Unfortunately, she’s had an insatiable blood lust ever since. Despite her condition, she’s been dying for a chance to feel normal. Last week’s episode saw her get bold and ask out Oliver’s campaign manager, Alex (Parker Young). According to the episode 7 plot synopsis on TV Guide, the show will tug at those strings a bit more before its major crossover event.

“Green Arrow’s ongoing battle with Damien Darhk gets complicated by a shocking revelation; Thea’s bloodlust returns and she loses control in front of Alex,” the synopsis reads. 

The consequences of revealing her secret to her new civilian friend aren’t clear ahead of the episode, but the network was willing to tease the big secret that Darhk is sitting on. Ever since Season 1 of “Arrow,” Oliver Queen’s partner, John Diggle (David Ramsey), has been on a side mission to figure out why his brother was assassinated. Previously, he learned that his little brother was involved in some nefarious war profiteering and that Darhk’s organization, H.I.V.E., had Andy Diggle (Eugene Byrd) killed to get rid of the competition. Now, according to the preview for the episode, posted below, it’s revealed that Diggle’s revenge mission is actually a rescue mission. 

That’s right, after being presumed dead for several years, it turns out that Andy is alive and under the thumb of Darhk. Felicity (Emily Bett Rickards) seems to think that he’s experiencing mind control of some sort, but it’s hard to tell if he’s a reluctant enemy to Team Arrow or just a regular one.

It seems like fans will just have to tune in to episode 7, “Brotherhood,” when it premieres Wednesday at 8 p.m. EST on the CW.