"Fear makes us do a lot of things that we shouldn't."
Barry sums up the theme of The Flash episode 15, titled "The Wrath of Savitar," quite nicely with that line. Savitar is back and fear becomes our heroes' guiding principle. Barry and Wally learn that decisions based on fear come with serious consequences. In this case, they play right into Savitar's hand and unleash his particular brand of evil back into the world. They also get Wally trapped in the speed force.
Last episode, after the gang stopped Grodd's gorilla army, Wally saw a vision of Savitar. The visions only grow more intense this episode. Cisco remarks that Savitar is "mind-punking" Wally. But he's only partially right, Savitar is "mind-punking" Wally — and everyone else.
Savitar's plan, as he reveals at the end of the episode, has been a patient long con. Unbeknownst to the gang, Savitar has been trapped in the speed force all this time. He needs two things to escape: the full Philosopher's Stone and someone to take his place. As you'll recall, Barry threw the stone into the speed force thinking he was getting rid of it. Luckily, Caitlyn kept a piece of the stone in the lab. Unluckily, Savitar devised a plan to get that remaining piece and a human replacement.
Savitar explains Flashpoint gave him the idea to turn Wally into Kid Flash to make him fast enough to replace him. Wally, trying to be heroic, mistakenly throws the remaining piece of the stone into the speed force and unwittingly gives Savitar everything he needs. Wally is then sucked into the speed force and stuck there for eternity — or until they save him. Cisco remembers a piece of Savitar's prophecy, "One will suffer a fate worse than death." Savitar, meanwhile, is now free.
Barry also learns not to make decisions based on fear. At the end of last week's episode, Barry proposed to Iris. But it turns out he did so hastily — he didn't even ask Joe for permission. Why propose so suddenly? Barry isn't telling us everything.
After vibing to see Iris' death, Wally discovers that Iris isn't wearing a ring when she dies. Wally exposes Barry's lie and points out that Barry only proposed so he could change the future. Iris is not happy and calls him out on proposing out of fear rather than love. "There's always going to be a part of us that's tainted," Iris tells him. "I want to be your wife, I don't want to be someone that you're trying to save for the rest of eternity."
There are still a ton of mysteries surrounding Savitar and his origin story. In their conversation through Julian earlier in the episode, Savitar reveals to Barry the gang is there when Savitar is born and he is who he is because of the Flash. During Barry and Savitar's battle, Barry makes a significant effort to see who Savitar really is — meaning Savitar has a true identity that will likely be revealed at some point. Regarding the question of Iris' death, Savitar plainly states, "You can't change the future."
Next week Barry enters the speed force to find Wally but meets the "ghosts of his past."
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