If there’s one trope that always works well in fiction, whether it’s on the screen or on the page, it’s having your heroes double crossed by one of their erstwhile allies. Particularly in espionage settings, but also in the realm of pulp — be it private eyes duped by their comely clients or archeologists who choose the wrong friends — or even in superhero comics, finding out that guy or gal you’ve been depending on has been selling you out to the enemy always works for great drama, and great drama makes enjoyable stories.
Working in that double cross with background NPCs is easy enough, but what if the traitor is a player character? There’s a few ways to make this work, but they all need player buy-in, if you’re to make it work without honking off the character’s player.
The player knows from the jump, the group does not: Here the GM can work with the player early on to set up the parameters of what the turncoat is doing, how much they want to reveal to the players, etc. You could have a general idea — my character is a SHIELD agent working for HYDRA undercover; my character is a Cylon in the fleet, working to erode the stability of the Colonial fleet; my MI6 operative is secretly a member of SPECTRE/the Russians/enter bad guy group…
With this option, the people who need to know, know, and they can try to work together to make life difficult for the others in the group. The player is the accomplice of the GM in making things move. They can conspire out of game, or by notes/texts in game — did he just report the team to the bad guys, ensuring their capture?, and the point of this approach is to keep the others in the dark. You might give them the occasional hint — Agent Smith sure seems to disappear a lot at night. That hot blonde chick in the berth next to me was seen talking with someone in the corridor right before that bomb went off and disabled the FTL! the key here is to make it innocuous — something that should be easily explainable. You might give them the occasional perception check to see something out of place. Or you could just wait until the cinematically appropriate time, and drop the world on them, complete with the traitor helping out. “Suddenly, HYDRA soldiers swarm the room, before anyone can act, Typhoon strikes!”
For players — this can be a real blast to do. You get to influence the story in a way that is not obvious to all. You are, in essence, acting as a deputy GM — your actions and ideas can turn the storyline in a way that might advantage you over the other players…try not to take a competitive stance as the player, even if your character feels that way. You are working with the GM to make this a better experience for all.
The GM wants to make a character a turncoat at some point appropriate in the campaign: I had this happen in my ongoing Battlestar Galactica game, and it went well. The key was that I chose the character that made sense for this — he was the equivalent of an FBI agent, a conspiracy nut that believed aliens, or something, was infiltrating Colonial society. The more he and the others dug up Cylon conspiracies, the faster they seemed to cover it up. In the end, I used a background bit that had been established early on — the character had been in a car accident and was “modified” by the Cylons to broadcast his experiences, and occasionally fugued out for his handlers to make him do things without his knowledge. The player loved it and it was a great reveal and made for great drama.
Another time, I tried this without player knowledge, and they were less than enthusiastic about the idea. I let it drop. Similarly, a PC whose player moved away I turned into a traitor at an appropriate moment. It worked so well because the character had seemed to earnest and steadfast. They never saw it coming. The player, while agreeing it was a great plot twist, was not overly happy with it being his former character.
Players form attachments to characters, and these are an expression of the player’s agency in the game world (and sometimes, it’s the only damned control they have over things in their real life, too…) — get the player’s buy-in before you turn their alter ego into something despicable. Trust me on this one.
Players — if your GM comes to you with this idea, here’s a few things to consider before turning them down or buying in: 1) Does it seem like a logical twist? In other words, have your character’s actions or beliefs hinted that they might be susceptible to the influence of the bad guys? And can you see how they might have gotten your cooperation? 2) Do you think this could give the game more or less dramatic appeal? Will this be something you could play up for a while, or do you think the others will just magic missile your ass to your game world’s version of Hell? 3) Might it be appropriate for the character’s story to end that way? 4) Do you want to keep playing the character, or were you getting bored? Maybe this might give the character a new lease on life. Maybe it’s a good way to end the character and move to something more interesting. Maybe you are moving away and your character is a bit too integral to just conveniently disappear…
The whole group knows: This only works when you have players adult or good enough to not use their meta-knowledge to try an improve their character’s actions in the game. Here, you might allow the player to openly show how he’s screwing the others over, or still use the secret note route…but people know he’s built to be a double agent. You might use codas and little cut scenes to let the players know that Agent Smith is dropping a dime on them to the enemy. The point is — they know and don’t do anything beyond what their character might know because they enjoy watching the story unfold, even if it disadvantages them, because they know that adversity is part of the fun of having an adventure.
I say this works best with players who are “adult”, and that can be a loaded word but it is truth — some folks (see above) put a lot of emotional investment into their characters, are competitive, or want to feel in control…these sorts of personalities do not work and play well with this sort of approach to conspiracies. You’d be better off with the first choice, here. However, as gaming has moved away from the antagonistic relationship between GM and players, and the more narrative/storytelling idea of role playing has become more popular, I’ve found people are usually willing to separate their knowledge from the character’s.
Players — the advice here is simple: help the story and the fun along. Yes, it’s great to win all the time, but it’s often more interesting when things go pear shaped. You get to do heroic stuff.
Example: I had one player in my Hollow Earth Expedition China campaign that was not the brightest fellow. He was trusting, a sucker for women, and a jump first, try to fly next, think once he hit the ground type. The player knew that something he was about to do was going to get the character munched, possibly killed…but it made sense that he would leap before he looked, so he did it anyway. He frequently had to take a moment to “do what Jack would do”, rather than what he knew was the smart thing.
Be that player — make the character and the game sing, even if it means things don’t go so smooth. GMs — in game systems with plot/hero/fate points, this kind of play can be aided by — well — bribing the player (or “compelling” them in Fate). Give ’em points for going along with the script. You all win.
(Aside: Way back in the ’90s, I used to keep a couple of 3×5″ cards that had a few words written on them just to have a nice shorthand for players that were about to let their natural desire to shred everything, including the plot. One had HINT on one side, CLUE on the other for when they missed the obvious. The other said IT’S IN THE SCRIPT, which I used for one particular player…)