Society, by Alexander Cook

Greg Radcliffe & Kellan Garcia are FBI agents, and are after the trail of a subject that nobody can identify or describe. The agents only knew that the subject was called Alan Dennehy and was able to circumvent the most essential laws of human understanding. People that met him were not able to recognize him or describe him, they could not even say what they had talked with him, and he made sure that he would approach people when there were no witnesses around. The pursuit of this subject, and other impossible beings of our society, would uncover individuals that were inhabitants of our world but had one foot in the other side, in a place that only few could guess.