What is the main conflict in Death at La Fenice by Donna Leon?

Death at La Fenice chronicles Commissario Guido Brunetti's investigation of the death by cyanide poisoning of renowned German conductor Maestro Helmut Wellauer in the middle of a performance of La Traviata at the Venice opera house, La Fenice. Brunetti learns that Wellauer is a scoundrel. Worst, Brunetti learns that Wellauer was a pedophile, raping young girls of 12 or 13. Brunetti realizes Wellauer's wife poisoned him because he raped her daughter by a previous marriage, not killing him but causing him to go deaf. Wellauer takes the cyanide himself, after realizing his hearing loss is