The Hidden Blade Assassin's Creed in Depth

Differential Notoriety

The five targets in the Meeting Adjourned mission are dispersed in a small room with many guards, which makes this mission seem like an unlikely candidate for anonymous poisoning. Fortunately, the developers made an unusual choice in the design of this mission: The room is not a high alert area. Instead, they elevated the awareness levels of the targets so that they behave as if you were Notorious, which is functionally similar to making the room a high alert area - except that the developers did not change the guards in the room correspondingly. As a result, the targets and guards behave differently in this mission, which is what I exploit in this mission design to poison all of the targets while remaining unseen (no yellow bars) to all of the guards.

Memorize the appearance of the target that you followed to get to this room. He behaves differently from the other targets, so it is useful to be able to easily identify him later. His appearance will change each time you play the mission.

As you climb down the ladder, two of the targets will be able to see you. Lure one of them to the ladder, and then disappear from his view so that he "cools down" from his elevated awareness state. Poison him on the roof, and wait for him to die. Repeat this process at least two more times.

Sometimes the poisoned target will fall down from the roof, sometimes not. If he does fall down, the dead body will cause the most or all of the guards to leave the room in effort to investigate. The guards originally stationed in the room will not return if they leave. However, there is guard patrol and a guard post at the room entrance that may see the fallen body(s), so you still need to be a little careful as you climb down the ladder. This mission will be a little different each time you play it, so you will need to adjust the plan based on what happens in your individual situation. You may even need to carry a body from the roof and toss him down to the base of the ladder in order to rid the room of guards and reposition the remaining targets.

Remember the target that you followed to the room? He can see dead bodies, but he cannot see you unless you do something aggressive toward him (in which case he flees). It makes sense to save this target for last.

Quick Setup

Here is a quick way to set up the Meeting Adjourned mission. You don't need to actually follow the target, but you do need to keep within a certain distance, and you do need to maintain visual contact every 25 seconds. You can easily get to the room ahead of the target. It's tempting to kill some of the existing targets in the room before the last target arrives, but their deaths do not count until the last target reaches the room. If you kill them early, you will not be able to complete the mission.

Other Comments
I don't consider this to be a fully "mysterious" assassination. Since there are multiple dead bodies, it's pretty clear that this was a planned hit, even if there is no evidence as to how it occurred. Also, I typically don't let the target see me at all in a "mysterious" mission.

The differential notoriety strategy still works if you are Notorious. The bars for the targets will fill up faster than those of the guards. It's a lot more tedious to do it this way, though.