A dangerous treachery, with an interesting twist.
Like all cards in the "small encounter sets" for this scenario, it is added to the encounter deck upon reaching Act 2, but only in 4 out of 10 possible outcomes.
The first part adds a doom to a specific boss enemy, which can only happen during "The True Culprit" endgame agenda, and only in 2 of the 10 outcomes (so only 50% of the time ; because when this treachery is present, 2 out of 4 possible endings will feature a different boss). But when it does matter, it stings, and adds insult to the injury of the second part.
The second part is a hard Willpower test for either 2 horror or 2 damage (ouch), with the possibility of dealing the damage to another investigator instead of your own. Or, you can deal the damage to a Humanoid enemy, which is generally a bad idea in this scenario if the enemy is Innocent or if the police are present (they will intervene and attack you).
But ! on occasion, this treachery will come as a boon, giving you 2 testless damage against an enemy that you want to defeat... There are 4 such enemies in the basic encounter deck (including a mini-boss), plus 3 other bad guys in 50% of the possibilities when this treachery is present.
I mean, what are the odds of drawing this treachery twice in one Mythos phase while being engaged with the evil concierge, and almost killing him with it ? Apparently, not zero, as it just happened !