The particularly brutal rape assault of a sixteen year-old schoolgirl in a wooded common provokes Det. Chief Supt. Velyan (Frank Finlay) into employing unorthodox measures to catch the maniac. He listens intently to Doctor Greg Lomax's (James Laurenson) rudimentary profiling technique in the hope that it will give him insight into the man's behaviour, which is obviously intensifying and escalating when a second schoolgirl is both raped and murdered. This time the killer was careless, however, as Julie West (Suzy Kendall), the school's art mistress, saw him when he drove into the Common in pursuit of his second victim. Putting her own life in extreme jeopardy, she sketches the face she saw and determines to catch the killer.