So I've got an encounter I'd like some opinions on:
My players had previously thwarted an assassination/theft attempt involving some cultist thieves (who died horribly) and an erinyes (who escaped). The erinyes has since been promoted into a pleasure devil (Fiendish Codex II, basically a pumped up erinyes with more abilities focused on manipulation, like beguile). This ambush is planned for as soon as the PCs return from their mission in the wilderness.
My group is 3 11th lvl characters: a human fighter/wizard/spellsword (complete warrior), a human ranger, and a halfling ranger/halfling outrider (complete warrior). The ambush will occur in a crowded street or just outside an inn, anywhere with lots of bystanders. The baddies consist of the pleasure devil (CR11), a tiefling illusionist 9 (CR 10), and one or two bearded devils (CR 5 each). The plan is for the tiefling to throw down a darkness globe in the surprise round (which they're almost guaranteed to get), the bearded devils to teleport in and start hacking randomly, and the pleasure devil to observe gleefully while polymorphed and charm bystanders to run into the fray, causing more bloodshed. Further rounds will put down another darkness globe , and the wizard to maybe lob some spells in like fireball. The goal is to hurt the group badly, but not kill them all. With the amount of cityfolk who will die (especially with a fireball spell...burning building maybe), and the pleasure devil trying to charm/beguile the PCs into hitting innocents also, the city guard will have some hard questioning and possible imprisonment for the group. The fiends will try and cause as much damage as possible before a) the guards or other adventurers show up b)1 PC and an animal companion are dead c) the darkness gets dispelled and a bearded devil dies.
Do people think this is too vicious/not enough/will cause fits? I'm also looking for any opinions on how the guards might treat the PCs; even if they prove that they didn't attack any cityfolk, the attack was obviously aimed at the group. Votes on imprisonment, exile, aid?