*This article contains spoilers for season 9: episode 10.*
The tenth episode of The CW’s The Flash season nine is titled A New World, Part One: Reunions. It’s also a four-part series finale.
Barry’s timeline has come full circle, as he is suddenly pulled back to the year 2000, by a mysterious blue energy. Allowing him to see many familiar faces including life-long foe.
Allen begins to look for help; in order to see if he can get back home, so he that doesn’t cause further disruption to the timeline again. He is knocked off-guard by his number 1 arch-nemesis Reverse Flash, and luckily saved by his parents. Barry soon realizes that he has a chance to spend a day with his parents, one last time!
Reverse Flash (Matt Letscher) is there to seal both of their fates; as it’s the year that Barry’s mother was killed, causing his father to be framed for a crime that he didn’t commit and stranding Eobard Thawne in the past. However, Eobard’s original intention was to go back and kill Barry, to stop him from ever growing up to be the The Flash.

Running to the house where it all began, there now appears to be three Barry Allens there: both Eobard and our present Barry, who can also be seen crashing through the window from the very first episode.
Younger Barry is saved by this current season 9 version all along, another from season 1: episode 23, where he ends up time traveling into his childhood bedroom.
A mysterious blue crystal possesses Joe West

It was revealed in the series 8 finale, that a blue crytal ended up in a lab, in 2049. Now, this crystal is responsible for transporting people to different times as well as being able to possess Joe West. This entity claims to be from the dawn of time and seeks to make Barry suffer.
What’s happening with Eddie Thawne?

It turns out that Rick Cosnett’s Eddie Thawne has not been resurrected by some time travel scenario, he’s actually playing Eddie’s future relative currently named ‘Malcolm Gilmore’ (pictured on his I.D badge); who is an employee of Mercury Labs. Could this be the same lab in 2049? Update May 18: episode 12 has actually revealed that he is Eddie and he’s been resurrected by the negative speed force, to be the next Avatar.
At the end of the episode, Cosnett’s character shares a similar incident to Barry in his lab; where he is struck by lightning and gains speedster abilities. This time something sinister is manipulating him to seek justice for Eddie’s death.
In the comics, his real name is Malcom Thawne aka Cobalt Blue and he will be suiting up for the finale, alongside other speedsters.
Cobalt Blue’s centre chest-piece of his costume also has that same blue crystal embedded. It now seems more likely that the crystal is also responsible for bringing back all of the other speedsters.
In a promo for episode 11; Barry is still missing and team flash are trying to figure out how to get him back.