"I'll go with the spell." You don't trust any potion the mi-go might give you.

"The words, steel rose, are Hei! Aa-shanta 'nygh!," says the mi-go. "But the words alone are not enough. You must read them from a spellbook." With that, it climbs back into the box of dryer-sheets and goes back to sleep.

Fortunately, you know where to find a spellbook.

Yeah, it's a plot contrivance. Deal with it.