The Theatre of the Tormented was a book written by famous author Gordon Edgley. He would later regret writing it as it it was basically an instruction manual to summon Demons.
"This was in one of Gordon’s books. The Theatre of the Tormented. Five friends try to summon the devil. Whatever they summon, they trap it in a circle. The main character, Eamon, gets away, but the others are killed. Then the demon thing tries to lure him back to drink his blood—"