a monster recognizes another one of its kind - this reminds of of the Joker in the Dark Knight - "Don't talk like one of them. You're not! Even if you'd like to be.".

Perhaps it would have been better if they'd moved on and tried to change. After all Rust calls it a 'debt' rather than 'unfinished business', and the catalyst for them to re-engage is two other detectives picking up the pieces much later anyway. I'm just not sure it would've been easily possible given how much of the case, of the 'demons' they'd already absorbed.

The reason they halted the pursuit was due to personal issues anyway, caused by Maggie seeking revenge. It doesn't just stop the investigation, it causes Rust (the real powerhouse investigator) to give in to the nihilist impulse - "I quit. I'll send you a letter, yeah fuck this. Fuck this world man".

The loss of the notion of any kind of redemption following the death of his daughter causes him to give into the worst of his cynicism about reality, and lose motivation thus allowing the demons to keep spilling out. Marty even looks regretful when he does quit, as if he realises the level of impact that sequence of events has had.

I do think the storyline is a redemptive one ultimately, hence the line possibly lifted from Moores work about the light winning. Marty saves Rust absolving him from blowing up his marriage (and sequentially his most meaningful career partnership), Rust equalises his demons and is allowed a near death experience validating the supernatural (an arguably necessary component for a non-materialistic worldview to sustain itself).

Thank you for the positive response too! I also think this is the best single show I watched in a long while, not since The Wire had I wiped my eyes in disbelief at the intelligence with which a show treated its audience. Discussing it is an immense pleasure, and you have given me a very fresh perspective.