Roy Morgan is a brilliant but diabolical murderer who eludes capture by eavesdropping on the police radio frequencies. It starts when Roy shoots and kills a patrolman when Roy is suspected of being a burglar. There are no clues. Police detectives Marty Brennan and Chuck Jones are assigned to find the killer. Roy obtains his electronic equipment from Paul Reeves. The detectives find  Roy’s frequent visits to Reeves suspicious. When they ask Reeves  to name  the mysterious visitor, he confesses that it’s Roy Morgan. Roy commits an armed robbery. The police are able to get one of the bullets and take it to Lee, a forensic specialist. Lee reports that the bullet he examined came from the same gun that murdered the patrolman. The detectives now know the murderer and close in for the arrest. What ensues is a heart-stopping chase in the Los Angeles drainage tunnel system. The film was shot in a film noir style and was the inspiration for Jack Webb, a cast member, to produce his highly-successful TV series, “Dragnet.”