I think he did drink something. He felt something before those two guys said they slipped a drug on his drinks. The real placebo was he's fine after the prof told him it was just placebo. I could be wrong
Chapter 10 is sooooo satisfying. The audacity of that Duke to threaten Opal with divorce is unbelievable. Dude your dukedom should be long gone if you didn't marry her.
The Duke is not even hiding his motives. Visiting them at their room. I mean what business does he have with 5-year olds?