Where we last left off, the PCs had gottem themselves thrown in prison, (the apparently infamous tower of Balun-Mar). The plan is that the campaign will start something like 10 years later, with the PCs breaking out of prison. What I plan to happen is to have a powerful NPC basically assault the prison in an attempt to kill another prisoner, and then the PCs will be able to escape in the confusion (and perhaps encounter this other prisoner, which could lead to all kinds of fun quests--I haven't worked out all the details, though I plan to run the escape as an adventure. It isn't just a deus-ex-machina "you escape").
The issue is, the party currently consists of a psion, a wilder, a binder, and a barbarian. Now it makes sense that the barbarian can be kept locked up (though I'm sure it takes a couple of guards to keep him down), and similarly the binder can be kept at bay by simply not letting him draw the signs to make his pacts. However, keeping a psionic character from manifesting is a bit harder. You can't just take away their spell components like with a wizard or sorcerer). The idea is that this prison was built for all the nasty bad guys, so the guards would definately be expected to be able to keep a psion under wraps. But I'm trying to figure out how they would do that.
Ideas I'm considering:
* Have an area of the prison that is wrapped in a permanent null psionics field. Because it will be a PbP, I could easily run the psions separately until they meet up with the other party members. However, I'm not sure I like this idea, as it would suggest that there is (or was) a psion around powerful enough to create a permanent field, which I'm not positive I want to have. I could also have the field be a "natural" effect of the area the prison is built in, which might explain what it was put there in the first place.
* Some kind of null-psionic handcuffs. Either literal cuffs, or maybe a collar that they cannot easily remove. I kind of like this idea better, as it makes the challenge more than just "get away from the area" to "how do we get these things off?" Also, theoreticallly the characters could then take the item with them, and use it in the future perhaps.
* Some kind of personal-level effect. Like maybe a power is used (and reused) on them that makes it nigh-impossible for them to manifest. I kind of imagine maybe the warden as another psion, who spends his time manifesting this power every few days/weeks to keep the prisoners in line.
Any other thoughts? What do you guys think I should do with this? I don't want to totally lock down the psions (though it might be neat if there is an encounter where they can't use their abilities), but I need some kind of reasonable explanation for why they haven't blasted their way out of the prison over the past 10 years.