That's the thing tho, I was thinking the same and was very exact doing that.
My order of doing things went - Overhear convo at Emily House, Go to Giron house, hide until dinner, go spy on Dave and Frisha, leave wait outside for next day/or go to house to sleep for next day, wait till 10 head off to bookcase to spy on Dave and Giron at 12, hit Hide and listen, it triggers a scene instantly and then listen to Dave and Giron. Then I wait for the next chance to go and spy on Dave and Frisha. Nothing
The convo between Dave and Giron goes - Dave wants help to sleep/corrupt Frisha asks Giron for help, Giron agrees and says "I can't help you with that... But I'll think of something ok?" Dave then says thank you and scene ends.