A failed assassination attempt on the Kingdom of Albion's queen causes spies on all sides to be questioned on their loyalty to their respective alliances. Amid the increasing tensions, Ange le Carré, Dorothy, Charlotte, and Chise Toudou have returned with a new assignment: to collect an antique bookstore owner held captive at the kingdom's prison. However, this simple mission is soon followed by fear when Control assigns the team to investigate a suspected double agent within the royal family. Ange and the other members of Team White Pigeon must face betrayal and bloodshed as they attempt to make contact with another spy while aware of only one thing: their codename, Bishop. The film is set in London at the end of the 19th century and after the attempted assassination of the Imperial princess in the television anime. The Empire is increasing counter-spy actions in the wake of the incident, and finds Control, the Commonwealth group in charge of covert operations against the Empire, at unease and suspecting its spy within the royal family as a double agent. Control assigns their spy ring Dove with a new mission to extract a secondhand bookstore owner and deliver him to Commonwealth hands. Ange, Dorothy, and Chise successfully spring the bookstore owner from an Imperial prison. Control also assigns Dove to make contact with Bishop, their spy within the royal family, to ascertain their loyalties.