Espionage is a gameplay mechanics included in the Civilization V: Gods & Kings expansion pack. Reflecting quite well real-world spy activities, this mechanics introduces a new level of covert actions in the game, which will have effects on technological advancement, diplomacy and even City-State relations.
Spy recruitment and mechanics
Espionage starts in a game once any civilization enters the Renaissance Era - when philosophers such as Machiavelli finally do away with the ideals honor and decency, and nations realize everything is permitted in war to achieve victory. Whenever the first civilization in the game enters the Renaissance, every player recruits their first Spy at the same time. After that, whenever any civilization enters a new Era, they get an additional Spy. Also, building the National Intelligence Agency provides an extra Spy for whoever built it. Spies are recruited automatically (within the previously described conditions) - they don't need to be produced in a city, they simply appear in their Secret Hideout.
Spies can be moved into cities from their Secret Hideout. You can only target cities you've discovered on the map. The movement takes only 1 turn (regardless of the city location on the map). After that, they take 3 turns to establish a surveillance network (5 turns for 'Making introductions' in case the Spy has been assigned as a Diplomat), after which they start their activities in the selected city and continue until given different orders. As of the Fall 2013 patch, if you have the influence level of Familiar, your spies will take only 1 turn to establish surveillance. This bonus also applies to higher influence levels.
Spies may die during their activities (Killed in Action). This happens when they try to steal a Technology and encounter an enemy Spy doing counter-intelligence, or when they organize an unsuccessful coup in a City-State. Killed spies are replaced after a few turns by new recruits.
You may boost your Espionage and counter-espionage by building certain buildings or wonders - the Constabulary and the Police Station diminish the success rate of enemy spies attempting to steal technology in the city where they're built by 25% each; the Great Firewall World Wonder makes technology theft in your whole empire close to impossible, and the National Intelligence Agency National Wonder levels up all your existing spies and decreases the effectiveness of enemy spies, besides giving you an additional Spy.
In Civilization V: Brave New World, any Spy can be requalified as a Diplomat when you station him into the Capital of another civilization. A Diplomat has different uses from a Spy, mainly related to the new World Congress feature, although he may still be able to monitor the other nation's activities just like a Spy. Note that a Diplomat can go back to being a Spy by moving him again (the dialogue opens each time you move the Spy).
Note: Both spies and diplomats abhor military action. Whenever you attack and capture a city where a spy is active (or when the enemy does the same), they immediately leave the nation for the Secret Hideout, where you can later re-dispatch them. The Diplomat, on the other hand, will be immediately withdrawn if you declare war on the nation he is serving, or vice-versa.
Spy abilities and activities
What the spy actually does depends on where he's assigned to. There are four possible spy activities:
- Surveillance - If you station a spy to another civilization's city, he will establish a surveillance network in the city, besides giving you vision of the city territory within two tiles, and the ability to enter its city screen. Much more importantly, he automatically screens for the civilization leader's intentions and activities. He will then warn you about their plans (e.g. "X is secretly plotting against Y"), although depending on the spy's experience level, he might not find many details about those plans. You may then use the information to gain some advantage, for example by warning the target about the plot. Diplomats also confer these benefits.
- Technology theft - While in another civilization's city, your spy will also engage in stealing their technology. If the target civilization has no technologies you don't know, you'll receive a message, "Agent X can't steal from civilization Y because we've completely eclipsed them in research".
Pay attention to a target city's science potential, before assigning the spy there! This potential depends on the number of citizens, and the presence of any anti-spy building or counter-intelligence activity. The greater the science potential, the faster the spy can steal a technology. Once a spy has established a surveillance network in a city, he will automatically evaluate its potential.
Depending on the technological level of the target civilization, on the science potential of the target city, and on the experience level of the spy himself, he will steal a technology within a certain number of turns. This technology is one that the target civilization already has, and you have yet to discover (but have unlocked).
Be careful, though! In the turn when stealing the technology, the spy exposes himself to a certain degree. If he's inexperienced, and the enemy has good counter-intelligence measures in the city, they may discover the theft and who's responsible for it, leading to diplomatic outrage. Also, if there is an enemy spy in the city, doing counter-intelligence, he may discover and kill your spy, preventing the theft.
- Election rigging - Stationing a spy in a City-State will set him to rig the local elections which occur regularly every 12 turns. If he's successful, the new City-State government will be more friendly to your civilization, and less friendly to others, meaning you'll gain Influence with the City-State, while others will lose it. Enemy spies may also be acting in the same City-State, and then the spy with better experience will have better chance to rig elections. Other bonuses may improve chances at rigging elections.
- Coup d'état - While in a City-State, your spy may also stage a coup. This is only possible when the City-State already has an ally. It is a dangerous course of action, because you risk losing your spy if the coup is unsuccessful. However, if successful, the City-State immediately allies itself with you, while their previous ally's Influence is reduced to the level of Influence you previously had on the City-State. The success rate of the coup tends to depend on your spy's experience level, the presence of other spies in the City-State, and your current Influence level with them (the higher your Influence, the more chance of success, because your spy may use the existing sympatizers to bolster the coup attempt).
Staging a coup may be the only way of gaining a City-State as an ally when their current ally has enormous Influence and you have no practical hope of eclipsing it. It is also the only way of getting out of war with the City-State if you're already at war with their current ally.
- Counter-intelligence - Stationing a spy in one of your own cities will have him doing counter-intelligence work. Whenever there is an enemy spy acting there, your spy will have a chance to discover and kill him.
Leveling up your spies
Every spy can gather experience while acting, and reach higher levels. He starts at level 1 - Recruit. He then moves to level 2 - Agent, and finally, to level 3 - Special Agent. For each higher experience level, the spy becomes more effective - He takes less turns to steal technologies, has higher success rate of election rigging and coups, and better chance to discover enemy spies (and kill them).
Leveling up occurs each time the spy successfully steals a technology (whether or not he's partially discovered), or each time he kills an enemy spy. Apparently, rigging elections and staging coups aren't that important.
As of the Fall 2013 patch, Spy activity may benefit from your cultural influence with the target civilization. When you reach influence level of Popular, all your Spies there act as if they were effectively 1 level higher than their actual level; at Influential they act at +2 levels!
Espionage may become very helpful to your civilization, if used wisely. If your science output is lagging, station one of your Spies in the capital of the fastest technology-developing civilization, and start making up for your low science output by stealing techs! If, on the other hand, your research is going pretty strong, and few other civilizations can match you, station your Spies in key City-States to gain influence with them. This is very important when pursuing a Diplomatic victory, but it could also be useful in many other cases. Also, don't forget to spare a spy (or two) to be stationed in your Capital (or one of your other cities with high potential) to make sure no one steals your technologies.
Diplomats confer additional options, allowing you to speed up your Tourism Tourism on other civilizations, or to trade votes with them for the World Congress. In the hands of skilled players, these may turn into crucial advantages!
The English civilization is especially effective at spying, because they get an extra spy as soon as any civilization enters the Renaissance Era. When playing as England, you should make sure you are using this advantage and expand it.