So, would now be a good excuse to perform a divination of our own? Not necessarily one targeting the Merlin, but maybe something more generalized. We know that there are no traitors among Langtry's entourage, but we didn't ask for the names of Nemesis hosts, and I don't think our Crown would have identified them as such if they weren't actually working against the Council yet.
To avoid burning future Crown questions, we could use Mac's pub as a focus to ask if anyone present, or anyone who they know or have interacted with, is a victim of Outsider possession or control. That not only covers the WC crew, but also Harry, who has met Thomas' girlfriend Justine, IIRC?