VANCOUVER, British Columbia — Arrow is less than halfway through its fifth season and has already dispatched one major villain, with last week's episode bidding farewell to crime boss Tobias Church (Chad Coleman).

Unlucky for titular hero Oliver Queen (Stephen Amell), there are plenty more bad guys to pick up the slack — including Church's killer, Prometheus, who now knows Oliver's secret identity, and probably doesn't intend to use it to send the vigilante-turned-mayor a fruit basket.

In episode 6 of Season 5, "So It Begins," airing Wednesday night, "we begin to explore why Prometheus is doing what he's doing," Amell told reporters on the Arrow set last week in Vancouver.

"And to explore why he's doing what he's doing, we actually have to go back in our story, which is interesting and something that I'm very proud that we're doing in our fifth season, because we're calling back to a lot of familiar parts of our early days in the show."

Prometheus isn't the only one digging into Oliver's past — reporter Susan Williams (Carly Pope) is now aware that Oliver spent some time in Russia five years ago, during a period when he was believed to have been stranded on the not-so-deserted island of Lian Yu.

"Susan appears to be up to no good, but in reality, she's just following a very interesting story. I mean, the mayor of the town where she is a news reporter was clearly not on an island for five consecutive years," Amell pointed out.

Despite her professional stake in digging through Oliver's dirty laundry, Susan also seemed interested in pursuing the mayor in a less official capacity last week. Oliver just discovered that his ex-fiancee, Felicity (Emily Bett Rickards) is dating someone else, so is he ready to move on?

"I don’t know if he’s ready to move on, but it’s time for Oliver to have another relationship," Amell said, noting that despite the writers' penchant for describing Oliver as a "billionaire playboy," he's actually been pretty monogamous, having only seriously dated one woman since Season 2.

"I’ve had a couple of scenes with Carly, who’s doing a great job as Susan Williams and I do think that there will be some exploration of a certain element of romance between the two of them, and I hope that people enjoy it because I’ve found it to be really dynamic so far," Amell said.

Oliver's time in Russia serves as an entry point for another villain — the formidable Konstantin Kovar, played by Dolph Lundgren. Amell gave reporters a little insight into working with the action star, best known for his roles in Rocky IV, the Universal Soldier franchise and The Expendables.

Dolph Lundgren as Konstantin Kovar Image: Katie Yu/The CW

"It’s interesting watching someone that has cut their teeth in film walk onto a 23-episode-a-year television show with 14-hour days, because he just moves at his own pace," Amell said. "It’s not indulgent; when he came to set, he knew his stuff – not that I expected anything less – he was very respectful, he asked a lot of questions, he’d clearly done his homework, but Dolph moves the way that he moves and he’s very thoughtful and contemplates his lines. He’s been great so far, but it’s a real change of pace. I do think that it would’ve been a missed opportunity in the last year of these flashbacks to not have a really worthy adversary, and we’ve found that in Dolph, which is why he’ll be around for a while. It’s been a blast to work with him."

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