Who is The Enemy from Cold Fire and what is their importance?

A membrane of wet, malignant animation, the Enemy is beyond human experience or comprehension. It is insectile, arachnoid and reptilian at the same time that squirms and jitters with a tangled mass of spider legs. It has antennae, serpentine coils and roach like mandibles with multifaceted eyes and the fangs of a rattlesnake. It has claws and throbs repulsively as it crosses the boundaries between nightmare and reality, attacking Holly Thorne. The Enemy only seems to appear when Jim Ironheart is unconscious, until Holly realizes who The Enemy really is. Then the manifestations come at her in the bright light of day.

The Enemy is a manifestation of Jim's psyche, revealed when Jim and Holly spend a night in the windmill on his grandfather's farm. It is the embodiment of his rage and helplessness and surfaces in times of stress or when the events he is suppressing threaten to surface. The Enemy can manifest itself in a myriad of ways, becoming everything from a flock of birds to a throbbing wall, and even a monster that is a combination of every science fiction book Jim ever read as a child.