The spymaster is the member of the council responsible for all matters of intrigue and skulduggery. It is an informal position on the council. The position of spymaster is available to those vassals and courtiers who are either male or the ruler's spouse or mother, over 16 years old, not a prisoner, and not incapable. The male-only restriction does not apply for pagans.
Spymasters are given a small monthly salary and a monthly prestige bonus, and upon appointment the spymaster will gain a +15 opinion boost towards his or her liege. Characters with a high intrigue stat are preferred for this position. Spymasters can be tasked to do three things: scheme, build spy network, and study technology.
Scheme - The spymaster is sent to a particular county to scheme there. While the spymaster is in that county, the plot discovery chance modifier will be increased, with a higher intrigue stat yielding a greater increase. There is, however, a small chance of the thugs attacking the spymaster, potentially wounding or maiming him. The local noble may also be recruited for the spymaster's liege's faction, or dissuaded from joining factions hostile to the spymaster's liege.
This can be thought of as 'defensive spying'. Use it on your own counties to discover plots against you, and disuade the local lords from joining factions.
Build Spy Network - The spymaster is sent to a particular county to build a spy network there. While the spymaster is in that county, the plot chance modifier will be increased, with a higher intrigue stat yielding a greater increase. There is a chance the spymaster will discover rumours about the local noble, or uncover evidence of his or her corruption. The spymaster's liege will have the option to reveal the noble's indiscretions, blackmail them, or keep them secret.
This can be thought of as 'offensive spying'. Use it on other lord's counties to power up your plots or influence other locals.
Study Technology - The spymaster is sent to a particular foreign county to study technology. There is a chance the spymaster will discover technological advances there which are not yet known in his or her realm, and use them to advance his or her liege's technological advancement. There is a small chance the spymaster's attempts will be uncovered, and the targeted ruler's opinion of the spymaster's liege will fall and the spymaster will likely be imprisoned.
The spymaster of a Byzantine ruler is instead known as a Mystikos.