A bizarre alien presence invisibly sweeps through Chicago, killing a petty thief and a UFO nut. The alien or aliens have the strength of a hurricane, generate a massive electromagnetic field, steal lead and electronic equipment, and suck the bone marrow out of humans and animals alike. Kolchak must track the alien(s) from an electronics warehouse to an observatory to Lincoln Park and drive them off before they kill again. His camera seems to hold the key to the creatures' weakness, although initially Carl is wrong in guessing what the weakness is. Carl follows the aliens and manages to keep them from feeding on him before they depart once and for all.