- For episodes of the same name, see Invasion!
- "We're going up against a bunch of aliens, and you want to tell people that their lives might have been affected by time travel? One sci-fi problem at a time."
- —Oliver Queen
"Invasion!" is the eighth episode of the third season of The Flash, and the fifty-fourth episode overall. The episode is the second of a four-part crossover with the eighth episode of the season two of Supergirl, eight episode of the fifth season of Arrow and seventh episode of the season two of DC's Legends of Tomorrow. It aired on November 29, 2016.
When aliens called the Dominators attack Central City, Barry speeds over to Star City to ask the Green Arrow for help in stopping them. Realizing the battle against the Dominators is bigger than they thought, they track down the Legends, and Barry and Cisco create a breach to bring back a secret weapon – Supergirl. Once all of the super friends are assembled, they come up with a plan to attack but a shocking secret related to Flashpoint is revealed and suddenly no one is sure who they can trust. Meanwhile, Wally wants to join the battle against the aliens but Iris tells him he's not ready.
- Professor Stein is revealed to have a daughter following the alterations to his personal timeline in "Compromised".
- The way Barry asked for Team Arrow's help is very similar to the way he asked them on the previous crossover, "Legends of Today". In the same episode, Felicity wanted Cisco to let her take control in the mission as they were In Star City but in this episode since they were in Central City, she let him take the lead.
- Oliver mentions that Thea retired from being Speedy, she left Team Arrow as Speedy at the end of the events of "Schism" even though she returned briefly in "Legacy".
- When asked what he saw, Barry describes that it was "enough to give Ridley Scott nightmares", referencing the director of the 1979 film Alien.
- This is the first appearance of Martin Stein, Jefferson Jackson and Mick Rory on The Flash since "The Fury of Firestorm" (for Stein and Jax) and "Rogue Time" (for Mick), Ray Palmer returns after appearing on "All Star Team Up".
- It was revealed that Iris still had a crush on Oliver since "Flash vs. Arrow".
- The scene where Barry and Cisco recruited Kara was recycled from the Supergirl episode "Medusa". Barry and Cisco both mention the events of "Worlds Finest" especially when Barry and Kara's race was a tie.
- When Barry went to ask Team Arrow's help, Oliver asked him (rhetorically) if he needs help with another evil speedster. This is a reference to "Rogue Air", when Oliver helped Barry dealing with the Reverse-Flash. Barry begins to answer yes, because of Savitar, only to change his mind to tell Oliver about the Dominators.
- Barry notes that Vigilante was about to "Scarface" Oliver and Diggle. This is a reference to the infamous final scene of the 1983 film Scarface, in which protagonist Tony Montana fires a hail of bullets at his enemies.
- Oliver mentioned his parents' death, which happened in "Pilot" (Robert Queen) and "Seeing Red" (Moira Queen).
- The message from future Barry, which first appeared on "Shogun", is finally revealed.
- Diggle finally finds out that his son was a result of Flashpoint which Barry and Felicity found out in Paradox. in the same episode, Barry tells Felicity about Cisco losing his brother as being a result of Flashpoint, when Cisco tells her this, she doesn't reply giving a small hint that she already knew but didn't want to upset him.
- This episode marks the third time Oliver ran out of arrows during a fight. He previously did so in Arrow Season 1's "Betrayal" and Season 4's "Brotherhood".
- The hangar at which the heroes gather is a reference to the Hall of Justice, a headquarters for the Justice League.
- The name of Supergirl's Earth is finally revealed as "Earth Thirty-Eight", which is a reference to Superman's comics debut in 1938.
- HR claims that if he helped Wally to train, he would be "gone faster than humor in a Liam Neeson movie". This is a reference to how Liam Neeson tends to star in dark, gritty action films.
- Due to Flashpoint, the writer of the future newspaper was changed, and is instead written by Julie Greer, who in the comics is a reporter for KN News in Keystone City.
- When Barry asks Ray about Snart, Ray mentions Snart's heroic sacrifice at the end of "Destiny" which they forgot to tell Barry sooner.
- Ray mentions to Cisco that his new Atom suit is made of Old West Dwarf Star which the Legends collected following their adventure in "Outlaw Country".
- Caitlin tells Stein that she attacked her friends using her powers, referencing the events of "Killer Frost", Cisco still can't forgive Barry after the revelations revealed during those events and his actions trigger the later events in this episode.
- Wally runs at Mach 2, same as Barry did in "Fast Enough".
- Sara mentions her sister Laurel when she tells Barry that she wishes that she could have saved her from the events of "Eleven-Fifty-Nine" but she doesn't as she knows of the implications it could have on history and her friends in Team Arrow presumably throughout the rest of Arrow's Season 4.
|The Flash season 3|
|"Flashpoint" • "Paradox" • "Magenta" • "The New Rogues" • "Monster" • "Shade" • "Killer Frost" • "Invasion!" • "The Present" • "Borrowing Problems from the Future" • "Dead or Alive" • "Untouchable" • "Attack on Gorilla City" • "Attack on Central City" • "The Wrath of Savitar" • "Into the Speed Force" • "Duet" • "Abra Kadabra" • "The Once and Future Flash"|
|"I Know Who You Are" • "Cause and Effect" • "Infantino Street" • TBA|