This season, on The Flash, a new speedster named Zoom has been sending super-powered beings from one parallel Earth to another to try and kill the Flash. On top of that, Zoom has done his fair share of killing people as this season has progressed. The Flash team wouldn't be where they are right now without the help of Jay Garrick, who comes from the same world as Zoom.
Warning: Spoilers ahead for the episode of The Flash titled "King Shark."
At the end of the "Escape from Earth-2" episode of the show, Zoom reached through the portal between worlds and dragged Garrick back to Jay's homeworld. This was done with Zoom phasing his arm through Jay's chest, so there's a really good chance Jay is dead. Team Flash is distraught and there's nothing they can do. Zoom is gone and their friend is probably dead.
During the closing sequence of "King Shark," Zoom is carrying the seemingly dead body of Jay Garrick through his personal prison. Zoom drops Jay onto the ground, and then Zoom removes his mask.
The only thing he says is "well, this is a complication." Zoom is Jay Garrick? This could mean a plethora of things. We've already seen time travel exists on this show and two people, from different timelines, can be in the same place, at the same time. However, we also know there are more than two Earths, so this Jay Garrick could be from another Earth, even the one Barry Allen and Team Flash are on.
There's been one indication that Jay is Zoom, from the man in the metal mask in Zoom's prison. He gave Flash a message that was decoded as "Jay." However, just because Jay was revealed as Zoom, that doesn't mean fans have any more answers. If anything, this just opens up for more questions and theories.
The Flash airs on Tuesdays at 8 PM on The CW.