Birmingham Theory

[Des]

Spoilers for the whole game, and particularly some of the endings.

After you complete the game and get augmented, Agent X begins the secret debriefing “Debriefing 3204 Birmingham.” Assuming this is directly after the events of the game [1], it would imply two things: Sam was in Birmingham [2], and Sam’s job in Birmingham was intrinsically tied to their job in August. As for the latter, I consider the most likely explanation to be that the same traveller was in both Birmingham and August. This is further supported by Rayne’s comment that “[the possessed Yuri Harris] said he’d see us again. In August. Before we even knew it was a month and a place”. [3] Since Sam is directed by Agent X to work with Chief Dupont, is augmented when they successfully stop the rite, and is told by Agent X “Don’t confirm the existence of travellers”, I believe Sam’s job in both August and Birmingham was to stop the traveller. [4]
This leads to the question: what went wrong? In the opening of the game, Agent X alludes to “the dead girl” and says “What exactly were you thinking? You have one job. Don’t. Get. Caught.” Chief Dupont also alludes to an incident in Sam’s past, offering “a shot at redemption” if you assist him and promising to help you with “the problem” from “your old town”, assuring you “the coroner’s report is going to say the woman was dead when you arrived, not after”. Considering both of these allusions center on Sam’s culpability in the death of a woman, it seems likely they refer to the same incident. As Agent X confronts you about it right before he sends you to August and we deduced Sam was in Birmingham chasing the traveller, this incident would’ve taken place in Birmingham.
The issue here is that the tarot readers don’t mention anything of the sort. Rayne in particular describes what happened in detail, yet there is no mention of a shapeshifter killing a woman; only three women were killed, and they were decapitated by the traveller who possessed Yuri Harris. To address this contradiction, I propose that Sam killed one of the traveller’s targets in Birmingham and proceeded to frame the traveller for her demise.
Since Agent X states Sam got caught but there is no mention of a shapeshifter in Birmingham, I suggest the woman Sam killed was the one who caught them. Perhaps she threatened to reveal their secret, and Sam struck her in a panic. Agent X knows Sam was caught while the tarot readers do not, so Sam likely informed Agent X themself [5], either in good faith to report the incident or to request help in covering it up. In any case, Sam successfully framed the traveller and Yuri Harris was blamed for her murder. If we assume a rite cannot be completed if one of its targets is killed by someone else, this also explains why the same traveller appears in August: having failed to complete the rite in Birmingham, it had to attempt another [6].
To answer the question of how Chief Dupont would be familiar with an incident that occurred while Sam was assuming a different identity, I would like to begin by proposing Agent X contacted Chief Dupont on your behalf. Supporting this, Sam is not shown nor instructed to contact Dupont before travelling to August (Agent X merely says “You’re going to a town called August. Find Chief Dupont.”), yet Dupont is expecting you, having already booked a room for you at the guesthouse and sent a message requesting you come to his office. [7] He also has a vague familiarity with your situation; in addition to his allusions to your past, he “suppose[s] you're between jobs at the moment”, and notably, he immediately rejects your introduction as Sam, stating “we both know that’s not true.”
Chief Dupont assumes you’re aware of the terms of your arrangement (“If you help me out, I’ll help you. … Do I have to spell it out? I’ll make your problem go away.”) and makes no reference to speaking with your superior or another such figure, so it seems reasonable to conclude that Agent X spoke to Chief Dupont in Sam’s name. Agent X thus introduced himself as a detective and agreed to help with the case on the condition that Chief Dupont would assist a detective caught up in a recent murder. Since Chief Dupont was not a witness to this incident that took place in “your old town”, he doesn’t know Sam was operating in a different body as well as under a different name; thus, he could easily come to the conclusion that Sam is a false name assumed by the same detective trying to cover up their involvement in the prior murder.

[1] as whether or not you see it depends on your choices in the game
[2] naturally under a different identity, but I will continue to refer to them as Sam for simplicity
[3] If Rayne is the killer and you tell Bronwyn the victims had gold coins in their mouths, she’ll remark “I should have known, that’s the same as Birmingham. Although they beheaded the victims, they all had gold coins in their mouths”, which adds credence to this theory for this particular timeline.
[4] However, I don’t believe Sam themself is a traveller, since when Violet dies while possessed, her corpse is identifiable, but when Sam dies, theirs is not.
[5] unless Agent X is omniscient, which would resolve this in any case
[6] Rayne does say “the traveller can’t come back when it can’t fulfill its rite”; however, we could take this to mean it cannot return to the same vessel or it cannot return to the same location.
[7] This message was presumably sent through Violet, since she tells you to go see the Chief when you arrive.

[Harley Rider]

Wow! Excellent job there

[Des]

Thanks! Happy to share some things I've thought too hard about, haha.

[Catafessi]

Would you please just add a giant spolert alert and make the text visible? I can't go past the second line for readability reasons.

[Des]

Fixed the formatting!