The alien Dominators land on Earth, and Barry realizes that he can't fight them alone. He summons Green Arrow and his teammates, and then the Legends, and then Supergirl from her Earth.
However, the discovery of future-Barry's message forces Barry to reveal that he may have altered all of their lives when he changed the timeline, sowing the seeds of mistrust.
The Flash Season 3, Episode 8 - Invasion!
Air Date: Nov 29, 2016