The archfiend of the series is a throwback to Tzeentch from Warhammer. Architect/weaver of fate, grand schemer, plans so convoluted they turn in on themselves for the sheer sake of it. The same archfiend that Adelt met when he was a boy.
Adelt is a trojan horse. He engages in self-deception and lies habitually. He believes his own bs so much it's hard to catch him in a lie. Everyone in the group calls him out on it, repeatedly. but he's too steadfast in his convictions, they start to believe it themselves. An agent who doesn't know they are an agent can't be thwarted by conventional means.
I suspected from the start, mostly because I'm genre saavy, and dislike the rogue archetype, but I really became convinced when he confessed to loving Flamie. He's playing her like a fiddle, hitting every weakpoint she's got. And she knows it, but can't resist because she was programmed in a similar way to Adelt.
That being the case, they both might be fakes, leaving Tanya as a real one, who's been corrupted.
Near as I can tell, the cow girl is the only real chance they've got since although she is an acquaintance of Adelt's, she wasn't taken in by his bs at the temple. She is on friendly terms with him, but she hadn't fallen into the trial of confidence the others were taken in by.