How is the "Moral High Ground" Mission Card intended to work?
Missions score at the end of your turn, after taking actions such as playing agents.
Although reveal isn't defined in the rule book, they do use it in the context of revealing cards from your hand. You cannot reveal an agent unless it is in your hand.

Moral High Ground: {1} for each killing or turning agent you reveal from your hand.

The Turn Sequence section states:

Turn Sequence - On each player’s turn, they have to perform 2 actions. Players can select from any combination of the following (including performing the same action twice);

Playing an Agent [...]

Re-activating a Command [...]

Buying an Agent or Mission: [...]

Trade in a Mission [...]


At the end of their turn, the player whose turn it is collects their intel points from their Factions and Missions. Players collect intel points from their Factions and Missions each turn as long as the data-tokens remain complete on their Factions and the conditions of the Missions remain fulfilled.

Although the conditions of the mission don't say when they must be fulfilled, I would argue that all the other mission conditions require checking at the end of the turn, so should this one. (You might also argue that to fulfill the conditions, you must continue to reveal the killing/turning agents until the end of turn, or you stop fulfilling the conditions. I.e. You are no longer revealing them.) Scoring of Missions also repeats the conditions must be fulfilled at the end of turn:

Scoring Intel Points - Intel points are awarded:

to players who have completed arrows facing them in their Factions at the end of their turn,

when the condition of a Mission is fulfilled at the end of their turn,

to players towards whom the points are directed when a Free Agent is played.