So recently while running a game of Dark Heresy one of my players concluded based on the available evidence that the individual they've been tracking could be a 4th generation genestealer. They explained to the other players that even though they are Ordo Hereticus it's important that they make sure to confirm this detail. Listening to this deduction I immediately conclude that their theory is really cool and that it would make for a crazy twist.
This is not case in my notes. The clues in the investigation just so happened to cause a player to come to this conclusion. I'm tempted to change things on the fly but a part of me recognizes that solving the case can be very rewarding. If I change the imporant evidence of the case on a whim it's kind of a breach of faith that it "could be solved".
What do you think? Cool to switch things up so long as they're none wiser? Or would you call it railroad GM fiat?
(Also bonus question)
I know a bit about genestealers but I don't know all the details.
4th generation genestealer (so nearly completely human)
1. Do they have to be bald?
2. Genestealers are psychic and can be directed and controlled by the patriarch. Does this mean they don't have free will?
3. Could a 4th generation genestealer be unaware that they are a genestealer? (Say the patriarch is thinking deep cover)