Oliver Faces An Alternate Timeline While Team Arrow Faces "Invasion!" In 100th Episode

The CW has revealed the official synopsis for "Invasion!," the hundredth episode of Arrow -- but even though that much has finally been revealed, it seems likely there will continue to be disagreement about just what kind of threat Oliver and company will face.

According to the official synopsis for the episode, Oliver will deal with an alternate timeline, while Team Arrow faces off against The Dominators, a race of aliens who will be terrorizing everyone in the DC Universe starting with November 28's episode of Supergirl and running through December 1's episode of DC's Legends of Tomorrow.

You can check out the full Arrow synopsis below:

ARROW CELEBRATES 100 EPISODES; THE EPIC SUPERHERO CROSSOVER CONTINUES — Oliver (Stephen Amell) wakes up to a life where he never got on The Queen's Gambit. Robert (guest star Jamey Sheridan) and Moira Queen (guest star Susanna Thompson) are alive and well. Laurel (guest star Katie Cassidy) is his loving fiancée and their wedding is imminent. Everything seems perfect, but Oliver starts to notice small imperfections that make him question this new reality. Meanwhile, Felicity (Emily Bett Rickards) and the recruits take on a new threat with help from The Flash (guest star Grant Gustin) and Supergirl (guest star Melissa Benoist).

James Bamford directed the episode with story by Greg Berlanti and written by Marc Guggenheim & Wendy Mericle.

How could this happen? There are at least two possibilities for how Oliver ends up separated from his team at this crucial juncture while they continue to battle on without him.

The first is that the world Oliver is experiencing at the start of the episode is his experience in the world of Flashpoint, and he's being exposed to it by Alchemy as a way of destabilizing The Flash's allies. This would gel with the official synopsis for the November 29 episode of The Flash, in which it's said that a big revelation about Flashpoint would leave the superheroes wondering who to trust. If somehow the Dominators were aware fo the events of Flashpoint, that could play into their attack strategy. Same for if Alchemy were to learn who Oliver Queen was.

The second possibility -- this one more driven by the Dominators themselves -- is that Oliver has been exposed to the effects of a Black Mercy. The alien parasite, which feeds off a host while preventing them from fighting back by creating the illusion that they've got everything they ever hoped for, played a role in the season 1 Supergirl episode "For the Girl Who Has Everything" and could be set loose on Oliver during The Flash to set this episode of Arrow in motion.

Supergirl airs Mondays at 8 p.m. ET/PT; The Flash on Tuesdays at the same time; Arrow on Wednesdays and DC's Legends of Tomorrow on Thursdays. All four series air on The CW. The "Invasion!" crossover will air beginning November 28.