 In an episode originally scheduled as the season opener (it was pushed back a few weeks to allow "Birthday Party," considered a better audience draw, to get the slot), a serial killer plunges a knife into anyone who stiffs him consumerwise -- six murders to date. The chief suspect is a troubled young man who sprays graffiti on walls talking about the character "The Grim Reaper." The young man is not, in fact, the killer (who shows up at the end of the third act in the shot-on-location footage), but gets a vicarious feeling out of the little guy fighting back. Kojak tries to enlist the young man to try to mimic the killer s thinking skills and stop him before he can strike again.