“Therefore She Is” is episode twenty of season four of The Flash.
Oxford University, 8 years ago, and Marlize is participating in a forum where she’s talking about the wonders of technology. DeVoe is also participating, and he disagrees strongly. In the present, Marlize tells DeVoe they have located everything they need. DeVoe says it’s time to retrieve it and enlighten the world.
A breach opens near Cisco and a box comes through. It’s a message from Gypsy; she wants to know his answer about taking Breacher’s job. Harry calls Cisco to the Speed Lab and Cisco puts the box into a drawer with others.
In the Speed Lab, they’re trying to get Killer Frost back. Cisco arrives to vibe Caitlin. Nothing happens and Harry says to increase power. However, Harry is clearly getting stuff wrong and he’s asked if he’s okay. Cisco tells them he isn’t.
Harry explains to the others what happened and that he’s losing his intelligence. He doesn’t know how long this will take. And then he won’t be able to help anyone. Barry thinks he can. DeVoe knew how to break them apart, but they’re still here and still family.
Marlize and DeVoe breach into Vandermeet Steel and gain access to a vault. Inside is Alloy 1771, which is what they came for. A security guard tries to stop them and DeVoe has him point his gun to his head. Despite Marlize asking him not to, DeVoe has the guard shoot himself as they leave, claiming it was the guard’s own doing.
Joe, Barry, Cisco and Iris arrive; Joe called the others because the only thing missing was something in the vault and the guard shooting himself had the smell of meta. Cisco is working out how they discover what was missing, but Barry zips around and works it out. He wants Cisco to vibe the guard’s gun to find out what the alloy does. Cisco doesn’t want to, as vibing and DeVoe don’t mix, and thinks there’s another way. Iris returns; it’s a solar metal that provides power. Barry thinks DeVoe is making something and still wants the gun vibing. Cisco says that would need him to double his power. Which makes them think of Gypsy.
Joe meets with Harry; he wants Harry to keep Cecille busy and he can’t say why because she’d just read Harry’s mind. And everyone else already knows. Joe also reassures Harry that the others will never stop trying to fix him.
Gypsy arrives and explains that she and Cisco need to be totally in sync. They vibe the gun and get a container at the port. Cisco, Barry and Gypsy breach there, but DeVoe is already there; it was a different container he wanted and he’s got it. DeVoe breaches Barry to the arctic and knocks the other two down., then breaches out. Gypsy and Cisco are arguing when Barry returns.
Cisco brought a piece of metal back from the shipping container in case they try to vibe it again, and talks to Barry about Gypsy and Breacher offering his job. Barry decides to help Cisco and Gypsy have a meeting of minds. Cisco does not think this will go well.
There are more clips from the past about Marlize’s relationship with DeVoe, and her discovering his idea of purging the world of human consciousness. He thinks humanity’s brains need rebooting so that they forget their crush on technology, because DeVoe believes technology is killing them. Marlize is initially not convinced. In the present, Team Flash is trying to figure out what DeVoe’s plan is.