Game concept
Agents
The game also links it as Agent.
From the game's encyclopedia
An Agent is a participant in a Scheme, who can provide one of three benefits. They can increase Success Chance, reduce Phase Length, or improve Secrecy. Only the target's Courtiers, Guests, and Direct Vassals can be recruited as Agents.
For Hostile Schemes, having agents close to the target is very important. For example Councillors or Close Family of the Scheme Target contribute more to Phase Length and Success Chance.
Being an Agent in a Hostile Scheme is a Crime, and Agent risk being Discovered.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Agents is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "An Agent is a participant in a Scheme, who can provide one of three benefits." It is part of Scheme. The game also links it as Agent. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.