[@Lucius Cypher] Warlock and Zealot can use tier 2 and tier 3 magic with INVOKE. Tier 2 spells take -1d on the roll and Tier 3 spells -2d, as well as costing stress to cast. 
Everyone else can attempt to INVOKE at tier 1. Spell lists are examples too, so you can make up your own if nothing quite suits perfectly. 
If people get too stuck with a way to go and are set on a Trickery Raid Plan I'll be happy to provide magic suggestions to navigate this problem but I don't want to influence your decision making too much if it can be helped

[@POOHEAD189] That would fall under your speciality, yep ;)