Inspector Knight was shot on an otherwise routine case. The bullet missed the vital organs, but nonetheless damaged his shoulder blade. The operation in the hospital gave him a steel joint so he could move his upper arm. Though modern medicine was quite miraculous these days, the joint didn't give him the full movement and rotation that his own bone and ligaments had.
More than that, the consequences of mortality had hit him with that bullet; to him, his days as a police officer were over. He retired from active duty on the force, using his ample inheritance to provide for his daughter. He spent more time with her, teaching her things like how to hit a baseball and the difference between a true democracy and a democratic republic.