Spoilish...
.
.
.
.
.
.
.
.
.
Yes, Invisible Stalker is VERY good. So is sending in a Demon (GATE spell, level 7 Priest)or Summon Fiend (Level 8 Wizard) If you don't have the level yet, use scrolls, they are not too hard to come by or buy. YOU MUST CAST Protection from Evil on party first, though, or they attack you, too.
And you need to check that the spell hasn't been wiped off your team by opposing magic, too. Make sure you have some single person Prot /Evil spells to top up individual team members. Also any spell armour and other protection from magic spells you have.
F.