The metahuman cure is finally finished and Team Flash decides that King Shark would be the ideal subject to test it on. The team travels to A.R.G.U.S. and requests of Lyla to get in contact with King Shark, who aggressively attacks the team under the mind-control of Gorilla Grodd. Barry reacts by injecting the cure into King Shark, turning him back into his human form - Shay Lamden. Back at S.T.A.R. Labs, Caitlin discovers that although the cure worked, there is still dark matter in Shay's pituitary gland and his body rapidly changes back and forth between his human and shark forms. Shay's wife, of Earth-1, Tanya, is convinced by Sherloque to talk with Shay. Later, Grodd mind-controls Cisco and Caitlin to steal Dr. Lamden's telepathy-crown to amplify his powers so he can control all of Central City. Seeing no other option and wanting to make amends for his crimes as King Shark, Shay gives up his chance of being human to help Team Flash stop Grodd; even in spite of the possibility of never being human again. Meanwhile, Joe returns home to Cecile and trains Iris to overcome Cicada who Barry suggests they offer the cure to instead of forcing it on him.