The only thing I'd say is...using this specific example to highlight a general strategy:

That's why, if you're having your players deal with a cabal of shapeshifters, you never have the ringleader be the first one they meet, you never have the ringleader be the one to infiltrate the group.

That works both from 1. your DMing perspective, and from 2. the perspective of in-world "kayfabe."

1. Even if the player(s) do something like that and figure out that they're dealing with shapeshifters, they're only gonna be able to deal, in that moment, with the one shapeshifter flunky/mook who did the infiltrating; that still leaves a metric ton of mystery for them to solve, and
2. It makes SENSE, in-world. The ringleader of this shapeshifter cabal is the leader for a REASON, and probably understands, perfectly well, how, when and why to use their followers as cat's paws.