So it sounds like we have a very lawful society bending lawful-evil beings towards lawful-neutral or even lawful-good ends. That opens a lot of fun story opportunities centering on the conflict between the demon-binders and the forces of darkness. You could go for an apocalyptic, end of civilization story, but I think running a game during this kingdom's golden age would be more fun. Here is a setting pitch:

The world is in a "Pax Romana" situation. There is no major conflict because nobody wants to fight an army of demons. Some small conflicts, proxy wars, rebellions, etc. are put down with relative ease. The kingdom is wealthy and the people are content but there are problems. Serious problems.

The bureaucracy of the government is bloating and doing more harm than good, leading to a lot of people going outside the system to get things done. The demand for goods is exceeding supply and leading to tensions. And the realm's politics are starting to get heated. The solution everyone has is the same as we've always had: summon more demons.

This leads to unsanctioned entities summoned by untrained casters and demonic manifestations become a serious problem. But we have to maintain control. The party's job is to investigate, contain, correct, and cover up these situations for the good of the kingdom and will answer directly to the inner court. Good luck.


Ideas for missions (a.k.a. 2 or 3 session adventures).

1) A low level bureaucrat has summoned a few imps to help in the office but he has lost control and things are getting out of hand. Dispel the creatures, arrest the idiot, make sure word does not get to the public.
2) There have been a few murder cases in the capital flagged as being suspiciously fiendish. Investigate them and deal with the situation appropriately.
3) A military commander has lost control of a demonic entity in a rebel controlled area. Re-establish containment and investigate the reasons for the breach.
4) The secret police have uncovered a plot to destabilize control of one of the outlying provinces and believe they are working with demonic forces to enact their plan. Your team was specifically requested for assistance in the case.
5) A rebel group is attempting to open multiple infernal portals in cities across the kingdom. Gather intel and disseminate it to the appropriate authorities to stop it in it's tracks.
This would obviously be more RP heavy but I think it would be fun. Sort of an X-File, James Bond, SCP crossover in middle-earth.