Arrest? On what charges? For what offense? If he can't attack an evil creature for being evil, how can he arrest her for being evil?That puts it somewhat into another light, altho I still think, that direct combat isn't appropriate. A paladin - at least - should first try more peaceful methods or at least try to arrest the druidess or something along those lines.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.