Katie Cassidy and Stephen Amell

Throughout its first season, Arrow has used flashbacks to show Oliver's growth from playboy millionaire to vigilante after being stranded on an island for five years. But what about his time before the island?

The CW series will finally offer up a glimpse at Oliver's pre-island life in Wednesday's episode as Oliver (Stephen Amell) and his now-deceased father Robert Queen (Jamey Sheridan) prepare to take a voyage on the Queen's Gambit — but this isn't the fun-filled and philanderous vacation that young Ollie was hoping for. "The pilot suggests that the Queen's Gambit's ill-fated voyage was just a pleasure cruise, but perhaps there was something more to it than just that," executive producer Marc Guggenheim tells TVGuide.com.

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We already know that the cruise ended in tragedy when the ship sank, claiming the lives of countless crew and Sarah Lance (Jacqueline MacInnes Wood), the sister of Laurel (Katie Cassidy), who was dating Oliver. Wednesday's flashback-filled outing will "explain how Sarah ended up on the boat instead of Laurel," Guggenheim says, adding that there will be a gut-punching moment when it comes to the sister switcheroo. "That's a big reveal in the episode," Guggenheim says. "And you learn what factors lead to Oliver cheating on Laurel."

But that certainly won't be the only thing we learn: The plans for the Undertaking will be laid out by Malcolm Merlyn (John Barrowman) during the hour. "Probably the biggest thing that will surprise everyone is just how much we explain everything," Guggenheim says of the episode. "This is really the episode where you learn everything there is to learn about the mythology of the Undertaking. We didn't leave any mysteries on the field. Everything is exposed and revealed leading up to the final two episodes. We wanted the audience to know exactly what happened and what is happening."

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When it comes to Malcolm's motivations for wanting to kill thousands of people, Guggenheim points to a rule the writers have lived by during this first season: Every villain is the hero of their own story. "We really started from a place of, 'Well, if he is going to kill thousands, why is he going to do that? How can he be motivated in such a way that we're consistent with this rule?'" Guggenheim explains. "Malcolm believes what he is doing is right. We think we've come up with a very interesting rationale that actually speaks to what Oliver's been doing for the past season and what a lot of heroes do. His motivations reverberate throughout the remainder of the season."

But Oliver facing off with the Dark Archer may be the least of his worries considering a logline for an upcoming episode states that Merlyn's son and Oliver's (ex?) best friend Tommy (Colin Donnell) "stuns Laurel with the truth." Does this mean he's going to reveal Oliver's true identity? "We began the year with this Oliver-Tommy-Laurel love triangle," Guggenheim says. "In the final three episodes, we're really driving towards a re-establishment of that love triangle. We're bringing that storyline to a boiling point. The story in this week's episode is really critical to that. Tommy's in possession of a lot of information regarding Oliver. It's information that has direct bearing on Tommy's relationship with Laurel. He has a couple different bombs that he could drop. What he tells Laurel about Oliver really will rock her world."

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Check out a sneak peek of a pre-island Oliver below and stay tuned for more Arrow scoop in the coming weeks! Arrow airs Wednesdays at 8/7c on The CW.