To those who haven't realized the significance of the Succubus' name, Avon...
Iniquity in Hebrew is “Avon” and means “to bend, twist, distort” so iniquities are bending, twisting, or distorting of the law of God’s Word. It really fits her character to how she bends, twists, and distorts people to her liking.
I also seriously believe Tom might have made a deal with Avon in some manner that involves what happened to MC. He seemed to known way too much about succubi and rushed into the library in a panic just as MC was being stalked by something. He then tried to deflect why he was even there.