Responses
You’re right. I once read a spoiler and it was him who poisoned Sylhan and Lysbet has been covering for him. That’s a major reason she doesn’t treat Sylhan as a slave despite it being his current official status. She probably harboured guilt from that situation. And the medicine Sylhan was being given by the previous physician was specifically formulated so that he doesn’t get his memory back. If he remembers, he’ll know it’s all Lister’s fault. That’s why they were so neurotic about Ida and the medicine she was prescribing.

I think all of Lister’s accusations are actually confessions, but I just can’t prove it yet.