Earlyfate by Nat Reeve

Sequel to Nettleblack
 
Pip Property is no stranger to disaster. Typically, they've got a plan, but now Dallyangle's favourite dandy & part-time criminal is locked in the morgue of the crime-fighting Division gone rogue, accused of far more crimes than they've actually committed, with (at least) two bucolic burglars out to strangle them with their own cravat. Their lover - the semi-feral Welsh heiress Rosamond Nettleblack - has disappeared into dangerous hands.

Enlisting the Division to save Rosamond might be Pip's only hope, but the cravat designer and the chaotic vigilantes have never seen eye to eye. The Division is looking to prove themselves to a potential new patron - and trusting schemers like Pip is a risk the detectives don't want to take. Armed only with a borrowed notebook, threadbare charm, suits without cravat pins and a swordstick everyone keeps confiscating, Pip must get the Division on-side, convince the Division that faith is a thing they can still have, and unravel the truth behind Rosamond's disappearance before it's too late.
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"An immersive joy: clever, propulsive, swaggering and beguiling." Nell Steven, author of Briefly, A Delicious Life