Dan's hit it on the head exactly, why he had a tendency to go off on his own and do what he wanted. He was better than anyone else the Church had at its disposal and they all knew it, which is why he got away with it for such a long time. Unlike a lot of exorcists, he was willing to bend and even break the rules if that's what it took to bring someone back.

"Only children?" he asks. That's horrible, of course, but he doesn't know any of these children. He does know Dan and he thinks by now they have a pretty good idea of what that monster wanted with Dan. What he wants with everyone he has.

Dan says they're gone, but Marcus knows there are other things that exist in this world who would probably want him just as bad.