How to continue the quest?It ask me to find incriminating evidence on the Baron Reedus,but i dont know what to do

also when talking to the baron about Bessie, nothing happens although I tried to talk to Bessie about her story

Exhaust all dialogue with Commander Cain and then climb the wall plants on the plantage to enter the mansion. Solve the wine bottle riddle inside and there you go.

The dialogue option is not available.