[3.5] Need help against an army of devils

[a typical hero]

Hello everybody!
Long-time lurker, first post.

I need some help to defeat an army of ghosts and devils in an unconventional way.

Line-Up:

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We're a group consisting of 4 lvl 11 characters.
Me (Wizard/Incantatrix/Swiftblade)
Bob (Cleric/Radiant Servant of Pelor)
Timmy (Warblade)
Bill (Favoured Soul)

vs.

Amount of x low level ghost minions
1 Adult or elder ghost black dragon
Amount of x medium level devils
1 Pit Fiend

Situation:

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The ghosts attacked a fortress where we wanted to reside for a few days.
In the mid of the uphill battle the devils joined us to fight off the ghosts. We decided to flee the scene and to overthink what to do next.

Now the devils are controlling the city and their leader (presumably the big Pit Fiend) is controlling the ghost army.

Solution:

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This is where I'm in need of your help.
I don't think we can defeat them oldschool by fighting against the whole city, so I came up with something more complicated.

I want to bring the Pit Fiend under my control via greater planar binding to command him to not harm any being on the plane for x amount of years directly or indirectly with his actions.

So..it goes like this:
1. Finding out the Pit Fiend's name
2. Summon him via greater planar binding scroll and trapping him within a magic circle against evil + dimensional anchor.
3. Dumbing his CH over a few days with geas, curse and enervation
4. ???
5. Profit

So what do you think about this plan? Suggestions? Better ideas?

[Mystral]

I don't think you can call a creature with that spell if it is already on your plane.

http://www.d20srd.org/srd/spells/pla...dingLesser.htm

[Optimystik]

You can clear the whole city with Banishment/Dismissal/Holy Word.

Also, the lesser geas trick doesn't work on Pit Fiends, too many HD. (Regular geas can affect PFs, but deals HP damage rather than ability score damage.)

[Riffington]

Perhaps there is some deal you can make with the ghost dragon?

[a typical hero]

Perhaps there is some deal you can make with the ghost dragon?

What could we offer the dragon to help us against his boss?

I don't know what it is that he obeys the fiend but I don't think my dm knows it either *sigh*.

[Kelb_Panthera]

Offer it the same thing you offer any ghost. Freedom. You agree to find out how to release the dragon from its ghost-hood and it backs your party against the pit-fiend. If that doesn't work, maybe use planar binding to call down a powerful celestial or three to sick on the PF. If you call CG celestials they probably won't even require much if any payment, for the task of destroying a PF. Of course that still leaves a ghostly black dragon to contend with.

[a typical hero]

I don't think you can call a creature with that spell if it is already on your plane.

http://www.d20srd.org/srd/spells/pla...dingLesser.htm

If we get into a rope trick first then it should be possible, right?

...

Sounds good to me. Sending should tell the dragon to meet us somewhere save so we can negotiate.

Thank you all very much, so far