Plot tumors are usually innocuous at first because they're not the worst part of roleplaying within a group. Usually, everyone comes in with characters that have a lot of different backgrounds and opinions, and the plots that are running take shape as a result of what's fun to play and what isn't. That's normal. Your character's hatred for elves might not be as interesting to play with as his love of cooking, and his past in the Stormwind Guard isn't nearly as intriguing as his close friend lost in the wilds of Northrend. Some character hooks don't fully pan out.
What happens is that over time, your character's lost friend becomes more and more interesting. You devote an event to it, and it's really interesting, everyone loves it, and so on. So you devote another one to it. Then other people start altering their character backgrounds to tie in or sometimes even outright abandon other character goals to chase this. Before long, the only thing your group is dealing with is That Lost Guy in Northrend, and every other plot is shelved or abandoned in flavor of this plot.
And however much fun it might have been in the beginning, now it's out of control. It just keeps growing, eating up other character interactions, and one decent plot among many has become an overriding imperative.
Needless to say, this is bad. It doesn't just hurt the sense of verisimilitude, although there's that too. It stops any new players from feeling invested in the group. Instead of a lot of running plots without the same core players, one constantly expanded plot produces a lot of backlogged events to catch up on, and it essentially promises new players that they aren't going to be more than bit members. It drains creativity, forcing every single event to lead back to the same road. And perhaps worst of all, if you manage to see it to its bloody end, you're left without anywhere else to go.
Just like real tumors, plot tumors are best spotted and excised early before they can take root and pollute everything you enjoy about a game. So the question then becomes how you spot them early enough that the operation doesn't kill the patient. Unfortunately, they can be hard to spot when you're in the middle of them, and often, by the time you manage, it's too late. So you'll have to be proactive.
An easy question to ask yourself is what your character would be involved in if you excised this plot immediately. If the plot no longer existed for whatever reason, would you still be telling stories with that character? If the answer is "not really," then congratulations: You have a tumor. Unfortunately, you also likely have one already too big to be excised without some serious work. The best you can do at that point is stop the plot train right away and start working double-time on new directions.
You can spot it earlier if events suffer from the circle effect. Look at how long it takes for a plot to circle back around to the old standby. In a healthy roleplaying environment, some things circle around to other elements, and some just don't. Your rogue is dealing sometimes with her children, sometimes with her on-again-off-again romance, and sometimes with her quest for a family heirloom. But if her romance has gotten tumorous, keeping an eye on what's going on around her might reveal that things circle back to that romance way too often.
With a proactive approach, you can make a tumor less likely to develop in the first place. If you've focused on one particular arc for a week, take a week off from it. Force yourself to let a story stand. Don't avoid moving it forward; just leave the plotline alone altogether. Do other things, pursue other plots, and try to make sure that it never becomes the defining aspect of your character's life.
In a previous column, I talked about giving conclusions without ending everything, but a plot tumor is the greatest enemy to that approach. It grows until that one plotline is everything to your character, and ending it would mean taking the character out back with a shotgun. Worse than that, it makes other people bored with both you and your character because everything winds up being the same story in a new set of clothes.
And that's your last and best defense -- ask other people. If you ask, "Are you tired of character X mooning after character Y," the responses you get are a great idea of whether or not you need to cut back. Ask early, ask often, and do everything you can to spot these things before they grow to be all-encompassing.
Feedback is welcome, as always, in the comments below or via mail to firstname.lastname@example.org. Next week, I'm going to take a step away from talking about problem characters or problem stories and talk about a very different sort of problem: players.
Every Friday, Eliot Lefebvre fills a column up with excellent advice on investing money, writing award-winning novels, and being elected to public office. Then he removes all of that, and you're left with Storyboard, which focuses on roleplaying in MMOs. It won't help you get elected, but it will help you pretend you did.