In Spidersilk the novel, Mark is visited by ghosts who try to invade his and his friend’s lives. These ghosts were from another dimension, but like the many theories revolving around ghosts, they probably needed energy to feed on in order to communicate. This energy could have been channeled via Mark’s aura as we know Mark had a strong energy around him throughout the book. This handy link shows a lot of interesting details about ghosts!
http://manchesterparanormal.org/Recharging-Energy.php