An actual Thief companion.
This is a wild tinfoil hat theory, but there could be a chance that Whisper may have something to do with it. Think about it:
- There are no other party members I can think of that has even something as simple as a sneak attack
- He's often (mechanically speaking, during his fights) hyped up to be your rival during the whole Tollus storyline
- Whisper is a lot more civil compared to the other cultists, and he may be using them as a means to an end.
I see him as a budding anti-hero type character.
Of course, you can just make your PC a Thief and do as you will, but considering that the companions in the game are supposed
to be made as "class representatives", I feel it's very strange that there isn't a Thief-type representative in CoC2, yet. You'd think
that would be one of the first things to implement, which makes me believe Whisper is somehow going to become one of the last
(even secret) companions you unlock in the game.
I may be horribly wrong about all of this, but these are just my two cents.