Me reading through Sherlock Holmes library for the first time (with the exception of hound of the Baskerville’s which I’ve read before): Strange. The mystery has been resolved but there’s still a good chunk of the book left
The villain: As you’ve bested me, mister Holmes and these constables shall surely take me to the scaffold, please let me tell you my humble life story in great detail.
I see it as Sherlock wanting a ‘complete’ accounting of what happened, which includes the relevant backstory.