The 2017 Arrowverse crossover “Invasion” was the creative team’s most ambitious crossover effort to that point. Not only did it incorporate multiple characters that debuted on Arrow and The Flash — with several who made their way to Legends of Tomorrow — it officially pulled Supergirl into the Arrowverse.
Though Supergirl is part of what’s designated Earth-38, she is recruited by Barry Allen and Cisco Ramon to aid everyone else in combating the Dominators, who have come to Earth-1 to eliminate its metahuman population.
The Dominators first land in Central City, where Barry Allen learns from Lyla Michaels more about them. Barry recruits Oliver Queen and members of Team Arrow, then members of the Legends, then Supergirl, to confront the aliens. In the Flash episode, many of the heroes are subject to mind control and Flash must find a way to free them.
The Flash episode brings the consequences of the Flashpoint arc in Season 3 of the show and forces Barry to confront that among the rest of the heroes. It’s Oliver who convinces Barry that he needs to stop worrying about what happened and tells him that he might have done the same things Barry did to save his parents.
The Arrow episode happens to be the 100th episode of that show, so the focus is on Oliver Queen experiencing an alternate reality in which he never became the Green Arrow. Oliver, John Diggle, Thea Queen, Sara Lance and Ray Palmer are abducted by the Dominators and subjected to this alternate reality, while Flash and Supergirl aid the rest of Team Arrow in securing technology that will allow Team Arrow to track down the location of those who were abducted.
Arrow does its best to pay tribute to its own show and the journey Oliver and his friends have taken, while addressing the main storyline of the crossover.
Legends of Tomorrow wraps up the crossover, which sees some of the Legends go back in time to learn more about the Dominators and their plans for Earth. Those who stay in the present learn the truth: the Dominators returned because Barry went back in time and they see him as a threat to the entire universe. Meanwhile, Cisco changes the timeline himself on his trip with the Legends and realize that, despite his good intentions, he may have done more harm than good.
The final episode resolves the Flashpoint arc and the heroes emphasize to Barry that he shouldn’t turn himself over to the Dominators just to prevent them from eliminating all metahumans.
There are a number of subplots that gets addressed along the way, ranging from Wally West wanting to become a superhero when he acquires superspeed, to characters other than Oliver confronting what life might have been like for them had Oliver never boarded the Queen’s Gambit — a choice that led to the events that transformed Oliver into the Green Arrow.
I think the crossover does a good job of balancing everything out, though admittedly it would have been nice to see greater involvement from Supergirl. It’s understandable, though, because the Supergirl series had just made its switch to CW and the creative team had to figure out the best way to incorporate Kara Danvers into the story.
But it set the stage for how all the heroes come to know one another and work together, leading to an even more ambitious effort in Crisis on Earth-X.
Invasion has its flaws, but holds up as one of the better crossover efforts and gave Arrowverse fans all the more reason to be excited about what the creative team could come up with next.