In the countdown to the season finale of "Arrow," the CW will air another all-new, intense episode of the DC Comics-based thriller this Wednesday, featuring a showdown between Oliver and Slade Wilson, aka Deathstroke.

When Oliver and Slade met for the first time since the island earlier in Season 2, Slade swore to uphold a promise he made to Oliver five years ago: "You cannot die until you have suffered the same way I have suffered. Until you have known complete despair. And you will." In turn, Oliver, tried to push his loved ones away to protect them from Slade, until he eventually let Sara in. He also promised to kill Slade and "make damn sure he stays dead," reports Hypable.

In the last episode, Frank Bertinelli purposefully got arrested in order to lure his daughter Helena Bertinelli, aka The Huntress, back into town. However, he ended up dying in the crossfire of a hostage exchange. Even though Helena was eventually arrested, "Arrow" executive producer Marc Guggenheim teased that this may not be the end of Oliver's crazy ex-girlfriend. "We definitely have an idea for a Season 3 episode with The Huntress," he told TVLine, adding that the writers went into the episode with the intention of killing Frank so that "we could start a new chapter for [Helena]." Plus, bringing back Oliver's ex-girlfriend "gave us a chance to articulate how far Oliver has come in his evolution."

At the end of last week's episode, Thea Queen found herself in danger after she and her boyfriend Roy broke up and she accepted a ride from Oliver's archenemy Slade. In the upcoming episode, which is aptly titled "Deathstroke," Slade will hold her hostage. Guggenheim also teased that "the sword of Damocles that's being held over her in [the next episode] is a double-edged sword - it's both physical and emotional - and I can guarantee that by the end of [Episode] 18, one of those edges is going to cut her." The EP added that Thea will learn "something pretty massive" in the next hour that "will cause a tectonic shift in her relationship with Oliver." Because the EP told TVLine that the number of people who know about Oliver's secret "will go up," it's possible that Thea will learn that Oliver is the Green Arrow.

During an interview with TVLine, Guggenheim went into detail about Thea and Roy's fallout, explaining that they had to breakup in order "to upset the apple cart. She is the only thing that keeps him in check. She keeps him grounded. It was also, if we were going to place Thea in jeopardy, we wanted Roy to feel some sense of complicity in that. Episode 18 is a very big episode. We sort of wrote it as a mid-midseason finale. In fact, when we turned in Episode 18 to the studio, the studio was like, 'You do know you've got to do five more episodes, right?' Episode 18 really could play as a season finale, just in terms of the number of things that happen and the number of cliffhangers that we're left with. And one of those things is Roy dealing with his own sense of responsibility in what's happened to Thea," he said.

Also in "Deathstroke," CarterMatt reports that Summer Glau's character Isobel Rochev will play an important role and that there's a chance that fans may learn more about her purpose and her plan.

The official synopsis for "Deathstroke" reads: "Slade (Manu Bennett) makes his move against Oliver (Stephen Amell) and the repercussions are enormous. While Oliver scrambles to protect his family, a key player in his team starts to question Oliver's decisions. Meanwhile, Isabel (guest star Summer Glau) makes her move to take Queen Consolidated away from Oliver."

The EP added that confrontation between Oliver and Slade will continue on throughout the remainder of Season 2 in "a series of showdowns."

"Arrow" S2E18, "Deathstroke," airs Wednesday, April 2 at 8 p.m. EST on The CW.

Watch a sneak peek below.