By Natalie Abrams
March 28, 2017 at 12:35 PM EDT
Bettina Strauss/The CW

Warning: This story contains spoilers from the first part of CW’s four-way crossover Invasion. Read at your own risk.

The Dominators have arrived!

During The Flash portion of the four-way Invasion crossover with Supergirl, Arrow, and DC’s Legends of Tomorrow, the technologically advanced aliens used a mind control device to turn the heroes against each other. But Barry Allen (Grant Gustin) was able to turn the tables, using the whammied Supergirl’s (Melissa Benoist) own strength to destroy the device.

In turn, the Dominators abducted Oliver (Stephen Amell), Thea (Willa Holland), Sara (Caity Lotz), Diggle (David Ramsey), and Ray Palmer (Brandon Routh), a precursor to Wednesday’s landmark hour of Arrow. The 100th episode finds Oliver experiencing what life would’ve been like if he had never taken that fateful boat ride, which explains the return of some of the show’s original characters who have since perished, including Moira Queen (Susanna Thompson), Robert Queen (Jamey Sheridan), and Laurel Lance (Katie Cassidy).

“It’s been five years since Oliver now didn’t get on the Queen’s Gambit, and he and Laurel are together,” executive producer Marc Guggenheim tells EW. “In fact, they’re about to be married. We basically pick up with them on the night before their wedding.”

Bettina Strauss/The CW

Alas, Oliver Queen’s wildest dreams have not come true. “These five characters are essentially being held in stasis by the Dominators,” Guggenheim says. “To keep their minds occupied, they’re in what we call a shared hallucination.”

While the Matrix-like construct feels real, the characters will begin to notice something is off about this new timeline, causing glitches in a system that’s otherwise perfect — a little too perfect for Oliver. But this provided the show an opportunity to look back on the last five seasons with an episode that offers some closure for those we’ve lost along the way. “The memory flashes that all the five characters experience, that gave us a lot of opportunity to revisit footage from the previous 99 episodes,” Guggenheim notes.

The Arrow boss says he takes pride in each of the show’s 100 episodes. “We never skimped on the writing, the production or in the post-process going, ‘This is going to be one of those stinkers, we might as well cut our losses and move on,'” Guggenheim says. “We worked as hard as we possibly can on the scripts. If episodes have come in bad, we reshoot. We’re going to pick up a scene for episode 510, not because the scene didn’t turn out well, but because there was just one moment that wasn’t landing the way it needed to land to pay off another moment. Even in season 5, we have no problems with doing reshoots, or pickups, or anything we need to do to make each episode as successful as it can possibly be.”

Bettina Strauss/The CW

But Guggenheim also admits he harbors some regrets. “The truth is, I don’t think I’ve ever been involved with an hour of television on any show where there hasn’t been something I wanted to take back,” he says. “Doing 23 episodes a year, you’re just constantly running, so nothing ever turns out exactly the way you want it to. In other words, my list of regrets is actually incredibly long; it’s 100 episodes long. I’d say probably my biggest regret is I wish we had allowed the Oliver-Felicity storyline in season 4 to unfold at a more natural pace. We had set these tentpoles at the beginning of the season, and we were a bit too rigorous on how we hit them. That was a case where the planning overtook the storytelling. We didn’t do things as naturally and as elegantly as we should have.”

Arrow‘s 100th episode airs Wednesday at 8 p.m. ET on The CW.