The Bourbon Arch

Conan and the detective boys get asked to investigate a strange tenant of the apartment building of one of their classmates. However, when they arrive at the apartment it has been burnt to the ground. That case is resolved but one of the other tenants of that apartment building, Subaru Okiya, a graduate student of engineering, or so he claims. It is actually Akai Shuichi in disguise. He intended to live in that apartment inconspicuously, but since it burnt down, Conan has him stay in his house next door to Agasa, where he can also keep an eye on Haibara.
Ran comes in contact with Okiya when she goes to Shinichi's house to clean. Conan tells Ran not to mention Shinichi's name around him. Shuichi doesn't know Conan is Kudo at that point, but finds out soon. Ran feels something strange about Okiya (as she has met him before in New York, as Akai Shuichi). At the end of that case, Okiya is seen drinking Bourbon (Hinting at Akai's identity). Also, just before that, it is learned from Rena who makes a call to Jodie, that they should look out for a knew member of the black organization who is supposed to be very smart, and great at obtaining information, who's code name is Bourbon.
This is the beginning of Bourbon's investigation into whether or not Akai is really dead. He is infiltrating the Black orginization, like Rena is, and like Hondo, and Akai did previously, but Bourbon (Furuya Rei) is with a different organization, the 公安警察の俗称, or the Secret Police. He has a grudge against Shuichi and the black organization, due to the death of someone close to him from the same orginization as him, who was killed by the black organization, when he infiltrated them, with the code name Scotch.
It is at this point that Vermouth probably meets with Bourbon to ask for his help in investigating Conan and Haibara (because the organization still wants Sherry dead. *NOTE: the organization doesn't know that Kudo and Sherry are Conan and Haibara. Only Vermouth knows, but is keeping it secret for some reason.) This is in exchange for her helping Bourbon investigate Akai's death. Bourbon also has secrets on Vermouth related to her relation to the big Boss.

In the next case Subaru is involved with, Haibara gets the feeling that she knows him(because he is Akai in disguise).