Creation and first use
Tanya Lamden constructed this device to stop the neural regression of Shay's mind (which was causing his mind to become less and less human, and more like a shark's). When Barry and his friends came to A.R.G.U.S. to visit King Shark, Tanya contacted Shay (who was in the water) using the device and a special set of earbuds she'd created to talk to him.
She informed Shay that a team from S.T.A.R. Labs had come to see him, having developed a cure for his condition, and he came ashore, asking if they really thought the cure could help him. However they all then heard a high-pitched feedback, then causing Shay to abruptly yank the telepathic crown off of his head, tossing it aside, and running off, causing Tanya to worry that Shay's neural pathways had reached a state where the crown could no longer help him.
Team Flash then brought the crown back to S.T.A.R. Labs, where they improved it, while also searching for King Shark. When they found him, Barry, Nora and Cisco suited up and went to the wharf where Shay had been spotted, bringing the cure with them to ask Shay if he'd like to try using it, putting the crown back on him when they arrived. However, Shay then suddenly grabbed Cisco; fearing Shay would eat Cisco, Barry quickly injected Shay with the cure, causing the latter to let Cisco go. Shay then fell backwards into the water, emerging as a human moments later. They then brought him back to S.T.A.R. Labs to rest.
Stolen by Grodd
When Shay awoke, they told him about the cure, but after running further tests, found that they'd have to inject him a second time for the effects to be permanent. Barry told Caitlin and Cisco to notify him as soon as the cure would be ready to be given to Shay again, but his two friends were upset that Barry intended to give Shay the cure without his consent. Suddenly, Cisco vibe-blasted Barry. Knowing something was wrong, Barry put Cisco in the Pipeline. When he got back, he found a mind-controlled Caitlin giving Grodd the telepathic crown. While Grodd escaped, Caitlin, still under the psychic-powered gorilla's control, hit Barry with a blast of ice as Killer Frost began emerging. Team Flash then realized what the feedback they'd heard before while trying to talk to Shay had been; Grodd attempting to take control of King Shark's mind.
It didn't take long for Team Flash to figure out what Grodd planned to do with the crown; the gorilla's powers allowed him to control only a few people at once, but the crown would make his powers a thousand times stronger, allowing him to control the minds of every human in Central City. Knowing that his more animal-like mind as King Shark kept Grodd from being able to control him, Shay asked that Team Flash turn him back into King Shark so that he could stop the evil gorilla. Team Flash warned him that if they did that, it may not be possible to make him human again, but Shay chose to go through with it, wanting to make up for the trouble he'd caused as King Shark. The two monstrous creatures then fought, with Shay ultimately emerging victorious, recovering the crown from Grodd.
Back in King Shark's possession
However, as Team Flash feared, they were unable to restore Shay to his human state after this. Shay then returned to A.R.G.U.S., using the crown to speak to Tanya, thanking her for everything she'd done for him, stating that he loved her.
The Chronicles of Cisco