In the late 19th century London, Team White Pigeon, a Commonwealth spy group, undertakes a new mission involving the delivery of a bookstore owner. As tensions rise between nations and suspicions of a double agent loom, Ange, Dorothy, and Chise must navigate a web of intrigue, including contacting the mysterious 'Bishop' to unravel the truth. Amidst escalating spy hunts and royal threats, the team faces the challenge of completing their mission and uncovering the identity of this enigmatic figure.