Watch 'The Flash' Season 2 episode 21 'The Runaway Dinosaur' live: Barry stuck in speed force, Black Siren debuts in finale

Barry (Grant Gustin) may not be able to justify the title of being the "fastest man alive," but he is sure to get his groove back by the end of The Flash" Season 2 episode 21. However, before that he will need to get out of whatever alternate reality he is stuck in.

Spoiler Alert

The upcoming episode of "The Flash" Season 2, titled "The Runaway Dinosaur," is directed by Kevin Smith and will see Barry stuck in a world which houses the people in his life, but aren't really them. In the promo, we see both Joe (Jesse L Martin) and Iris (Candice Patton), but it is clear that they are not the versions Barry loves back on Earth 1.

It is clear that Barry is stuck in the speed force, which features beings that exist outside space and time. They have taken on the physical appearance of the people in Barry's life and will not let Barry get back to his old life.

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In the promo he tells the Iris lookalike: "Please let me go back right now." The episode builds up in a way that Barry, who has lost faith in his abilities, will have to believe in himself to break through the speed force and return to his world. The efforts of Harrison Wells (Tom Cavanagh) will also hopefully help him.

The people back home, including Wells and Cisco (Carlos Valdes), will also have to deal with the return of Girder (Greg Finley) in the episode. The real Iris volunteers to act as bait, because of his obsession with her, as evidenced in his first appearance in Season 1.

This episode will hopefully end with Barry getting his speed back and the revelation that now Wally (Keiynan Lonsdale) and Jesse (Violett Beane) are also speedsters. The additional metahuman power would serve useful for Team Flash, considering Zoom will soon be sending a team of Earth 2 metahumans to Earth 1.

It is understood that the team would be led by Black Siren, the Earth-2 doppleganger of Black Canary (Katie Cassidy) in the Season 2 finale. She will hopefully have a long run on "The Flash," especially now that Cassidy's character has been killed off for good on "Arrow."

Don't forget to watch Season 2 episode 21 of "The Flash" at 8 p.m. (EST) on Tuesday, May 10. You can also watch "The Runaway Dinosaur" online via CWINGO and The CW Seed.