We open with The Flash and XS down on the ground knocked out, with Grodd and Shark above them, fighting each other.
We wind back to 12 hours earlier at Star Labs, where the cure has been completed. Cisco explains the cure is completely finished and they even have the way to get it into Cicada, but they still need to test it on a metahuman. They aren’t sure if it’s dangerous or not. They realize that someone on another earth may want to volunteer—King Shark.
The Team goes to visit Lyla at ARGUS. They explain that if they can reverse King Shark’s meta powers, they can do it for anyone.
Back at the West House, Cecile and Iris chat with a returning Joe West, who had been visiting Wally. Joe brings up Cicada to Iris, wondering if maybe he’s still getting help from someone. Iris doesn’t want to discuss the topic, so she leaves the room for more coffee.
Team Flash meets up with Dr. Landon (wife to Shay Landon from another earth, who is the human form of King Shark). She is working with King Shark, teaching him how to speak more through a telepathic crown. The crown also curbs his violent behavior. The Team explains they think they can cure him so Dr. Landon contacts King Shark and he comes to hear about it for himself.
They expect him to be open to it, but instead, he tears off his crown, knocks over Barry and runs away, escaping.
Back at the West house, Iris and Joe continue to discuss details about Joe's trip. Iris wants to work at the house for the day, but Joe brings up the new office, and Iris decides to head over there instead.
At Star Labs, Cisco and Dr. Landon try and find a way to catch King Shark. Sherloque points out that Dr. Landon may have feelings for King Shark, but she insists he’s just her patient. They get a hit on where King Shark may be, and head over to his whereabouts.
Dr. Landon connects to King Shark who has had the crown reconnected thanks to Nora. He still won’t listen, however, and begins to eat Vibe, so Barry has no choice but to stick him with the cure. It works, and he emerges from the water human.
Back at Star Labs, Shay (previously King Shark) starts to flip out, but Tanya calms him down. Caitlin explains that he is almost fully human, but there is still a small part of dark matter in his lymph nodes. Shay explains that he doesn’t really remember much of being King Shark, but should be held accountable for his actions none the less. He explains that his escape earlier that day felt different for him because the crown helps him remember. Right before he goes to grab Tanya's hand, he begins to transform back into King Shark.
Cisco and Caitlin confront Barry, frustrated that Barry isn’t interested in asking for Shay’s permission to give him the cure. They agreed that the cure would never be used as a weapon, and Cisco insinuates that Barry knew he would always force the cure on people instead of giving them a choice.
Joe finds Iris working at Jitters instead of her office. Iris explains that she feels terrified that Cicada now knows who she, and her family is. She feels powerless, so Joe decides to give her help.
At the Lab, Caitlin explains that he doesn’t remember what happened that morning because he experienced an extreme brain wave in his frontal lobe, which glitches his emotional and rationality. When Barry comes back to apologize about how he acted at the dock, Cisco turns and blasts him with a vibe.
Barry realizes that Cisco and Caitlin are being mind controlled so he locks up Cisco and goes to grab Caitlin but she freeze blasts him, and Gorilla Grodd appears, taking the crown before disappearing.
After Grodd leaves, Cisco and Caitlin’s minds go back to normal. They can’t find Grodd because his psychic abilities are keeping him hidden. Lyla explains how the night of the enlightenment, Devoe’s attack shut down power in ARGUS for one second, which allowed Grodd to mind control a guard into setting him free.
The team realizes Grodd was attempting to control King Shark earlier in the day, but King Shark was fighting against the mind control. Now that Grodd has the crown, it will amplify his mental abilities and he will be able to control the entire city.
Sherloque walks in on Tanya staring at Shay Landon. She claims she’s keeping her distance because of how Shay almost turned back into King Shark. Sherloque questions her about her reservations and suggests her real issues are stemmed in the fact Shay looks like her husband from her earth. Tanya explains how she can’t love Shay since he’s her dead husband's doppelganger. Sherloque explains that every person is unique regardless of their face.
Tanya then approaches Shay, and the two share an intimate conversation, where Shay admits that meeting Tanya changed his life. The two share a kiss.
Joe explains to Iris that Cicada didn’t break him, and he’s not going to break Iris, either. They start boxing training.
Cisco tracks Grodd to the center of the city where it becomes clear he’s going to get inside everyone’s head in the city.
Team Flash decides Flash and Nora are the best to go up against Grodd. Meanwhile, Grodd is already overtaking the city. XS runs as fast as she can around Grodd, while Flash punches him. He falls, and Barry goes to grab the crown, but Grodd wakes up and throws Flash across the street.
Shay suggests turning back into King Shark to save Flash and the people of Central City, but Caitlin warns him if he does this, he won’t ever turn back into a human again. Shay says he doesn’t care; he has to make up for what he’s done.
Cisco vibes Shay, turning back into King Shark and sending him after Grodd. After an epic battle, Grodd throws King Shark on his back, rendering him immobile. The Team decides to electrify him to get him moving again, as Grodd continues to mind control the city.
XS and Flash throw a lightning bolt at King Shark and knock Grodd off of the bridge. King Shark rises, now more powerful than ever, and destroys Grodd with one punch. He removes the crown and places his back on his own head.
The Team relocks Grodd up again, and they induce him into a coma so he can’t escape again.
Sherloque goes to visit Tanya who is watching King Shark swim. He insists that they will figure it out no matter what happens.
Iris goes to her office for the first time since Cicada attacked. She gets a text message about the Grodd vs. King Shark and she can’t believe she missed it.
At the Lab, Barry apologizes again for forcing the cure on King Shark and using it as a weapon and promises it won’t happen again. They accept his apology and celebrate the fact the meta cure works. Barry suggests that they should start with offering the cure to Cicada, and give him a choice.