In this episode, the hostage situation of Momiji Ooka on the Shinkansen culminates. Her butler, Muga Iori, a former Public Security agent, is blackmailed by the kidnappers to find a USB drive containing incriminating material about politician Tsurugi. The USB drive contains a video showing how Tsurugi's secretary was murdered, instead of committing suicide.

Iori discovers that the victim, freelance journalist Hirotaka Tanigawa, wrote a message in shorthand on his thigh with a pen, revealing the hiding place of the USB drive: his sock. Conan and Heiji Hattori, who have figured out the situation, find the USB drive and hand it over to Iori to lure the perpetrators into a trap.

Together with Conan and Heiji, Iori implements a plan in which he makes the perpetrators betray themselves by speaking more and more quietly. Heiji and Kazuha Toyama then overpower two of the perpetrators. A third accomplice, disguised as a train attendant, tries to take the USB drive and attacks Iori with a knife. Iori is saved by a stack of karuta cards in his breast pocket that catches the knife.

The episode shows a flashback that deepens the relationship between Iori and Momiji. Three years ago, Momiji saved the injured Iori's life during a raid on the family villa by bandaging him and turning off his alarm clock to give him rest. This experience prompted Iori to quit his job at Public Security and become Momiji's butler to protect her.

After the train arrives in Tokyo, all three perpetrators are arrested by the police. They were acting on behalf of Diet member Tsurugi, who is subsequently charged with murder. In parallel, Rei Furuya (Amuro Toru) receives a mysterious call from an unknown man instructing him to investigate Edogawa Conan to the core, hinting at future developments.