The coy smile on Campanella's face is growing bolder.
"I found the outline for a summoning spell - a ritual casting of old. Assuming it works it would draw down the Supernal enough to make contact with an entity from Stygia itself. The outline isn't a rote, though. Just enough to build the framework of an Imago; and one supposes the casting would be quite involved. Take a look yourself. These are my notes."
He drew folded papers from his coat pocket and offered them. A gamble, true, but Campanella had the original document in his keeping.
For reference, the spell is Summon Supernal Being (Summoners, p73 and following)