John is demonstrating his musical talents at The Sea when Rachel (from "Manifest Destiny") arrives to pay him a visit. They exchange a hug and Rachel prods John into taking her out on the town. After she leaves John panics about what he should do on their date. Meanwhile, at a music club a young up-and-coming DJ, Turney Scott, pumps up the crowd but starts to feel weak. He dives into the crowd but then collapses, blood pouring from his mouth and nose.
John goes to Frank for dating tips when they bring in the DJ's corpse and John deduces he was an epileptic and John concludes someone shut down the implanted anti-epileptic device that the DJ used. John then meets with Rachel to take her out to an Indian restaurant but he's clearly nervous. They agree on fish and chips and John takes her fishing off a pier followed by dancing.
John, Frank, and Stu go to the club and notice interference on the video recording. John notices a stray wire leading to a remote unit playing infrasound. They talk to Rachel who can confirm that infrasound can kill when properly applied. John and Frank meet with the DJ's girlfriend Charlotte who claims she wasn't aware he had epilepsy. John gets down with the band after displaying his musical talent but breaks a string.
They meet with the dead man's agent, P.J. Fox, who claims he wants the killer found, but begs off. Frank and John follow him to the club where the murder occurred. It turns out the agent is working as a DJ and he runs off when he spots them. They capture him and Frank takes him in for interrogation while Frank meets with Dr. Hillman (from "past Imperfect"). Together they work to hit John with over 13 million music files so he can try and activate some missing memories. John finally locks onto a memory of ragweed when hearing the song "My Funny Valentine."
Avery interrogates Fox who denies everything and says a lot of people wanted Scott dead. Charlotte brings Turney's old records in while Fox gives up the name of a guy, Lloyd Craft, who threatened Turney. They go to Lloyd's apartment and find he's an albino, and he reiterates that Turney stole music from him. John runs a vocal match of Lloyd's voice and finds him e-mailing threats to Turney. Rachel shows up for dinner and they explore John's memories by what foods he likes and dislikes. Rachel mentions she likes red licorice. When Rachel questions which world John wants to live in, past or present, she decides to leave him to it.
At Fox's office, a janitor is cleaning up and finds him dead, garroted with piano wire. They conclude he was killed while drinking with someone. They find an albino-type hair sample and go to arrest Lloyd. John works with Stella to isolate the ambient background of the killer signal and John determines it was recorded in a closed studio. He goes back to the studio where Charlotte worked and when she arrives he confronts her with how the killer used the amplifiers to record the feedback to make the infrasound signal. He relates how Fox figured it out and then Charlotte killed him too, framing Lloyd. She confesses and tells how she was Turney's lover until he started dating his groupies. Charlotte makes a break for it, locking John in the studio. He determines the shatter pitch of the studio glass and rigs the speakers to break it open.
Charlotte makes her way out via the roof while John calls Frank and goes after her. He sees a furniture mover using a wench to haul in a sofa and quickly calculates the weights to drop down and intercept Charlotte and capture her.
Back at police HQ Frank advises John to focus on the present rather than the past. John goes to see Rachel at her hotel room where she finds red licorice and follows a thread of it outside to where John is waiting for her, and they agree to try things out.