Vermouth and Bourbon keep close contact with one another, and seem to be closer to one another than, say, Bourbon and Gin. Bourbon specializes in intelligence gathering, so he likely belongs to the same reconnaissance division of the Black Organization as Vermouth. While it is still uncertain whether Bourbon is working directly under Vermouth, she seems to keep track of his actions during his missions at times,[38] and he also often informs her about his discoveries or his future plans.[39] Vermouth helped Bourbon create a disguise that looked like Akai so he can investigate his enemy's death. Later, she somehow helped him approach Kogoro because he suspected that the detective was in contact with Sherry. Bourbon made an unknown promise to Vermouth (possibly being to not harm Conan or maybe not to leak her secret to the other members of the Black Organization ) , and she calls to ask him if he will be upholding it after the car chase in Detectives' Nocturne.
The two have shown to be working together, not unlike Gin and Vodka, though the bond and trust between them are somewhat lacking. In addition to Bourbon's promise to Vermouth, he is also aware of her secret relationship to the Boss/Anokata, as noted at the end of the Scarlet Showdown. Bourbon utilizes this information to enlist Vermouth's assistance in his investigations, arranging for her secret to be released to the other members of the Organization Vermouth threaten to kill him if he decide to reveal it to the organization although decide not to after he told her that her secret will be leak to the organization if he dies.