The April 3 episode of "Arrow," titled "Unfinished Business," sees the deadly drug Vertigo -- and its creator, The Count (Seth Gabel) -- return to plague Starling City.

"Vertigo is back and more dangerous than ever," star Stephen Amell told The Huffington Post at WonderCon. "Because Tommy [Colin Donnell] and I have both had run-ins with the law based on drugs, when we find out that a girl got high on Vertigo in Verdant, I cast a suspicious eye his way and he does not appreciate it -- and nor should he."

Oliver's not the only one who's suspicious of Tommy -- Detective Lance (Paul Blackthorne) is too; and worse, he's the father of Tommy's current girlfriend, Laurel (Katie Cassidy). Awkward.

"He doesn't really like me in the first place, does he?" Donnell laughed. "There's an accusation from [Lance], and he doesn't exactly have his best friend sticking up for him right away, which really causes a big problem. Every relationship is tenuous right now, and this doesn't make it any easier."

Donnell admitted that Tommy will be feeling pretty isolated, especially as Laurel "has her own shit going on, and he's not there for her," the actor said. "She is there for him, but I think, because of the way that he knows that she feels about Oliver/the vigilante -- even though she doesn't really know how she feels about the two of them -- he doesn't think he can go to her in that way. And obviously he can't. He can't be like, 'By the way, Oliver's the vigilante.'"

One person that Tommy can rely on -- for the first time in his life -- is his father, Malcolm (John Barrowman). But since Malcolm is also the Dark Archer who has made several attempts on Oliver's life, things have the potential to get even more complicated.

"He's got his dad back a little bit now, and you see the Merlyns coming together," Donnell said. "In the opposite way from the way Tommy and Oliver and Laurel are sort of drifting apart, the one last person that he has to turn to is good old dad. Well, he's not good old dad ... Who knows if he would reveal himself to Tommy? And the big question is, how would Tommy feel about that, because that's gonna put him between a huge rock and a really hard place."

Oliver's relationship with Tommy isn't the only one under strain this week, as Amell revealed that our hero will also find himself at odds with crime-fighting sidekick Diggle [David Ramsey]: "It tests my friendship with Diggle, which is something that we're exploring," he admitted. "I've always said that I want him to be my partner ... except when he has his own ideas! So it puts a strain on our relationship."

Could that friction have anything to do with Diggle's vendetta against Deadshot [Michael Rowe], the assassin that murdered his brother? Last month at PaleyFest, Ramsey told us that Diggle's thirst for revenge might drive a wedge between the dynamic duo.

"The conflict is going to really be because he has a quest that may not fit into the quest that Oliver has, in terms of the list," he said. "Oliver sometimes makes decisions based off of emotion, like not going after his mother. Diggle, for the first time, is making an emotional decision about going after Deadshot, and he may not get the support that he would expect to get from his 'partner' in anti-crime. And that is gonna be a problem."

As for Diggle's plans for Deadshot, Ramsey had a few detailed ideas: "[He'll] try to rip his heart out -- good TV, ain't it? Diggle is on a bit of a blood quest for the heart, liver, spleen of Deadshot. And it's gonna be great drama, and he's gonna have to come face to face with some of the preaching he's been giving Oliver over the past season, of just, 'Be careful, you can't kill for no reason,' and now he has to hear it regurgitated back to him."

But as one partner rebels, another potential sidekick is discovering his inner hero. Willa Holland (Thea) revealed that after last week's encounter with the vigilante, Thea's boyfriend, Roy Harper (Colton Dixon), is "enamored with The Arrow," and the pair will embark on a "journey to uncloak Oliver without realizing that they're doing it. Roy is now on this virtuous path, so that he can go out and seek him and figure out who he is and maybe put himself under his wing. Thea is going to be helping him out because she's now definitely in love with this guy after everything she's gone through with him. They've jumped to this strong place very quickly and that leads to a couple of fights here and there."

Even with everything happening in Starling City, the episode will still take us back to the island to learn more about Oliver's evolving relationships with Slade Wilson (Manu Bennett) and Shado (Celina Jade), Yao Fei's (Byron Mann) newly-freed daughter.

"In the newest episode, Shado decides that she wants to train me, because we want to get back to Fyers' [Sebastian Dunn] camp and try to rescue her dad, and they can't do it just the two of them, they need me," Amell explained. "And we have no guns. So she wants to train me -- it's exciting. Her tactics are a little bit different from Slade's; Slade is a tough love type of guy, Shado's more teaching me ... I think I'm learning one thing, and I'm actually learning something else."

The Huffington Post caught up with Celina Jade via phone earlier this week to find out more about the mysterious Shado, who is a major player in the Green Arrow comics. Read on for our interview.

I hear that Shado's methods of training Oliver are very different from Slade's -- and his haven't worked very well thus far. How is Shado's approach different?
Well, as you know, she’s Yao Fei’s daughter. So, the way she learned martial arts is a little bit different. The way I would describe it is, it’s a little bit like Mr. Miyagi in "Karate Kid" ... She has a really different way of teaching martial arts. It’s almost like a philosophy as opposed to just, 'OK, punch, kick, do this.' It's a rounded way of coming to building his strength to become an archer, as well as a martial artist. So yeah, definitely very, very different from Slade’s tactics.

I'm guessing we won't have flashbacks within flashbacks on the island, but will we get an opportunity to learn more about Shado's backstory through other means?
Yeah, in Episode 19, Shado will have a conversation with Oliver about where she comes from and a bit about herself as well as Yao Fei. There will be a lot more backstory that comes to our attention in that episode.

What can you reveal about her past and how she ended up on the island?
Shado is the Yao Fei’s only child as China has the one child policy. Yao Fei was a high ranking Chinese military official, he was like a general. He was blamed for a massacre by the Chinese government and sent to the island as a prisoner. Basically, Shado was a lawyer trying to fight for a pardon to get her father back to China, but she’s failing. All of a sudden, men show up at her doorstep saying, “Look, I have intel on your father ... ” She lets her guard down and the next thing you know, she’s trapped on this island and kidnapped by these guys to use against her father, which you saw in Episode 14.

We know that Oliver spends five years on the island and their first meeting is still very early on in his stay. Do you already know the broad strokes of your character's arc and where she's going to end up, or are the writers giving it to you script by script?
They’re very good at keeping me on my toes. I’m just as excited as you guys are to find out where things go between her, Slade and Oliver. Obviously the island is kind of crazy and it’s very uncertain, so anything can happen right now. But yeah, I’m excited to find out her arc and what’s going to happen in the future.

Oliver and Shado have matching dragon tattoos, from what we've seen of Oliver in the present day, so we can surmise that their relationship must have been pretty intense. Can you preview anything else about their dynamic?
Yeah, it definitely is intense. Other than being his mentor, I can say that she’s the person who really believes in his potential and believes that he can become strong and fight and have a chance to survive on this island. Whereas, as you see in the beginning, Slade was like, "Well, you’re never going to survive. We’re all going to die." So ... definitely there’s a romantic tension between the two.

What's her relationship with Slade like, in comparison?
It’s kind of a bit of a "Who’s the alpha male?" tension between the two. There is definitely a flirtation going on from Slade’s side, but I’m not sure that Shado really gives into that. But there’s definitely a "Who’s the alpha male?" [tension] in the trio between Shado and Slade, which I actually really enjoy, for a female character to play equal to someone as strong as Slade.

You clearly have a lot of martial arts experience already, so how have the fight scenes been for you? Do you try to do your own stunts?
Yeah the fight scenes have been really fun. There’s an incredible team behind "Arrow," so I learned a lot of new moves and choreography. I do have a stunt double who helps me out with falls and moves that are more dangerous. She's absolutely amazing. I’m so grateful. It’s actually quite dangerous -- it’s raining in the forest; it’s slippery; there are a lot of rocks and stuff, but it’s good. I’m used to doing martial arts movies in the past so it’s not completely new. The only thing that’s a bit different for me I’d say is the weather. I’m not really used to it. In Asia, it’s quite warm and humid, whereas here, it’s quite cold. So what happens is, all your muscles tense up really quickly and you really have to keep warming up or otherwise, it’s really easy to pull something.

Did you have any experience with archery before taking the role?
Other than Club Med when I was a kid, I haven’t really done archery. My father was a really keen archer when I was a child, coincidentally. But his bows are 150 pounds to pull so I couldn’t pull any of his bows ... I really have very little experience with it. It’s been really cool. I’ve been taking classes and learning how to do archery as well as doing moves, moving around so you’re not just standing there shooting. It’s been so much fun I want my own bow now. I don’t know how I’m going to get it through immigration. [Laughs.]

Were you familiar with the comics before taking the role? Shado has a fascinating history.
I was never a huge comic book fan, but ever since I got the audition for Shado, I started to read online about her character from the comics and how it differs from her character in the "Arrow" series. So I’ve been learning more and more about the comic and it’s actually been a dream of mine to play a comic book character. So, I’m really, really excited. It’s so cool to play such a strong female character.

"Arrow" airs Wednesdays at 8 p.m. ET on The CW.

Are you excited to see more of Shado? Do you think Tommy's closeness with his father will be a good or a bad thing? Weigh in below!

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