There Is Only One

"You're familiar with the rules concerning exorcism, Damien?"

"Yes, I am," answered Karras.

Merin began buttoning up the cassock. "Especially important is the warning to avoid conversations with the demon..."

"The demon." He'd said it so matter-of-factly, thought Karras. It jarred him.

"We may ask what is relevant," said Merrin as he buttoned the collar of the cassock. "But anything beyond that is dangerous. Extremely." He lifted the surplice from Karras' hands and began to slip it over the cassock. "Especially, do not listen to anything he says. The demon is a liar. He will lie to confuse us; but he will also mix lies with the truth to attack us. The attack is psychological, Damien. And powerful. Do not listen. Remember that. Do not listen."

As Karras handed him the stole, the exorcist added, "Is there anything at all you would like to ask me, Damien?"

Karras shook his head. "No. But I think it might be helpful if I gave you some background on the different personalities that Regan has manifested. So far, there seem to be three."

"There is only one," said Merrin softly...

The Exorcist - William Peter Blatty