Irimina suggests that the Night Crows could make a very resourceful ally of Thaddeus Dusk if they help escort his daughter, Leah Dusk out of the city.
The general plan was two-fold, there would be two carriages leaving the Dusk estate - one would hold one of Thaddeus's most trusted allies as a decoy, and the other would be more plain and contain Leah.
The group decided to cover both carriages, sending Mirage to escort Leah personally, while Spanner and Duster would cover the other carriage.