A nice change of story but question:
How did he prove in the "last episode" that he is not the killer without saying who is the actual killer?
Did he just pretend that when he woke up he only saw the fire?
And ... why???
Well, Kate found them both imprisoned in that dungeon, so I am sure she told the others.
And if you are referring to Roald, he saw Joe freeing himself from the chains with a rock, and said "now me".
No, I'm referring to Joe keeping the killer identity a secret.
And yeah, Roald seeing Joe freeing himself might mean nothing, he could have just orchestrated all of that. Roald got knocked by Joe, then wakes up with Joe. It could mean that Jos is behind all that.
And what did they do about Gemma? They did try to hide her body which would be highly suspicious. Or did ALL of them lie about it? Would require some coordination between ALL of them.
Oh, yeah, the fact that Roald was unconscious until the very end made it very easy for Joe to pretend that he just woke up a little bit earlier.
As for Gemma, I thought her body burned in that fire. Not sure how they'll explain it - otoh, it seems like those people don't have to explain much.