At its core the main sleuth in this story is an interesting idea. A deaf man who is so incredibly competent, charismatic, smart, and massively sexy that everyone just wants to do what he asks. People respect the guy a lot and he's good at solving crimes because he logical (his skills work best in locked room scenarios). People just fall over themsleves for this Drury Lane or comment on how attractive he is. Also he's a master of disguise.
My issue is the pacing as said. If you set up that Drury Lane KNOWS who the killer is and then won't say you actually need to set up a better course of action then the attourney and police officer investigate random people because it feels like we are spinning our wheels. Lane knows who the killer is so investigating all these other people feels like a waste of time.
The ending chapter Lane actually reverses and says "Well I suspected but I wasn't sure if there were accomplices and we needed to get everyone" which.... you could have said that and kept the tension so we are left wondering if anyone else is in this conspiracy.
Also, the bigger problem is all the side characters and family members don't get real development. They're uninteresting which undercuts one of the strengths of a murder mystery which is outsized crazy character studies.
The solution to the puzzle is interesting. But to get there we have to tread so much uninteresting water.