Quinn's thugs have Casey, Sarah, and Chuck trapped on a bullet train in Japan. After breaking out of a locked container, Sarah finds Chuck and tackles Quinn and puts him in one of the containers. Chuck finds out that Sarah has the Intersect. With some time to kill on the train, Sarah announces the two of them need to start practicing more, if they want to start a family any time soon. She flashes to a scene of the two of them getting romantic.
Back at Castle, Ellie and Devon suspect Morgan's memory loss may be due to the number of times he flashed when he had the Intersect
Over at the Buy More, Quinn's thugs, posing as flu-shot providers, kidnap Alex (Mekenna Melvin) is quietly kidnapped by Quinn's operatives posing as flu shot providers. Watching from afar, Jeff and Lester wonder what's going on.
Quinn tells Casey they have his daughter, Alex, and tells him he wants Sarah and Chuck back, or else he'll have Alex killed. Quinn tells Chuck and Sarah he wants the Intersect. Sarah flashes and throws Quinn off the train. The flashes are getting to her and she develops an unbearable migraine. Ellie tells Chuck they need to suppress the Intersect, so Chuck steals electronic devices from train passengers in order to build a suppression device.
Morgan and Devon decide to rescue Alex using weapons stashed in Casey's car. When discovered, Casey must ask Lester and Jeff for help.When the two get Alex back, they demand Morgan tell them what's really going on. He complies and gives them a tour of Castle.
Quinn manages to get back onto the train and he and Chuck fight it out. Casey jumps in and stops Quinn from hitting Chuck over the head with a laptop. Then Quinn and Sarah fight between train cars and he shoots her with a tranquilizer dart. She passes out and wakes up in a warehouse. To escape, she sets off her emergency beacon. But when Chuck and Casey come to the rescue, she and Quinn are gone.
Then Sarah wakes up in a hotel room and she doesn't remember what's been going on. Quinn shows her a picture of Chuck and orders her to kill him.