"The Flash" season 3 episode 8 will kick off a massive crossover event with the entire DC television universe, putting together the Flash (Grant Gustin) with the heroes of "Arrow," "Legends of Tomorrow" and "Supergirl." "The Flash" is only the first part of the event, and the second part will be on "Arrow" season 5 episode 8.

During the first part, the Flash summons Oliver Queen, who is also known as Green Arrow (Stephen Amell), the Legends of Tomorrow, and Kara Danvers, also known as Supergirl (Melissa Benoist), to fight against the Dominators, an alien race invading Earth. In the second part, Green Arrow wakes up discovering his whole life has changed.

According to the official synopsis for the episode, as per Spoilers Daily, Oliver will wake up but discover he is now in a timeline where he never got on the Queen's Gambit. His parents are both alive, and Laurel Lance (Katie Cassidy) is now his fiancee.

Unfortunately for Oliver, this dream world will not last long, and he will discover that something about this reality is wrong. Just like how the "Flashpoint" event unfolded for "The Flash" season 3, it is possible Oliver will slowly recall the original timeline and struggle to find his way to go back to the reality he once knew.

The synopsis further reveals that while Oliver is trapped in this false reality, Felicity (Emily Brett Rickards) and the rest of Team Arrow continue to work with the Flash and Supergirl to defeat the Dominators or the Dominions.

In the original DC comic books, the Dominators were a unique alien race who were masters of genetics that could even alter their genes to race their caste in Dominion social structure. They have attempted to invade Earth on multiple occasions in the comic books.

"Arrow" season 5 episode 8 will air on Nov. 30. The "Invasion" crossover event will then continue on "Legends of Tomorrow" season 2 episode 7.