Following the increased activity of the CUCW (Council for the Unification of the Communist World), a new division of COSMIC (Commonwealth Offices of Security and Military Intelligence Co-ordination) is formed with the code name SCU3. A 'Hunter' agent (No. 5) is assigned to SCU3, and his first assignment is to investigate the mysterious suicide of scientist Dr. Brian Tolhurst, who was working on an anti-missile project. Following a lead that Tolhurst's car contains evidence of foul play, Hunter comes within seconds of death when CUCW agent Kragg plants a bomb and blows the car up.
Hunter learns that Dr. Tolhurst had a secret association with showgirl Rosie Glow, and she now becomes the only lead in the investigation of Tolhurst's death. Hunter and Eve Halliday go undercover and follow Rosie to Surfer's Paradise. While scuba diving, an attempt is made to kill Rosie by Brisbane CUCW agent Jim Bettman, and Hunter combats a shark to save her life.
Rosie Glow confesses that she helped CUCW agents fake divorce evidence against Dr. Tolhurst. Bettman plots Hunter's death in an aircraft accident, which Hunter thwarts by clinging to Bettman's parachute as he jumps from the plane, and Kragg makes an attempt to kill Rosie.
After Bettman attempts to kill Hunter in a plane crash, Hunter overpowers Bettman and takes him to Melbourne. Mrs. Tolhurst gives Hunter a letter that asked her late husband to visit Solomon, an opal dealer in Andamooka, South Australia. Solomon has been under suspicion for espionage work at the Woomera rocket base.
Mrs. Tolhurst and Eve are kidnapped and held aboard a yacht in the port of Melbourne by CUCW agents, who use a doll repair shop as a cover to retrieve microfilm hidden in the eyes of toy dolls. Hunter is tricked into visiting opal dealer Solomon at Andamooka, where an attempt is made to kill him in an abandoned mine.
Hunter tries to prevent CUCW agents Kragg and Zhadov from sabotaging the Prometheus anti-missile weapon at the Woomera Rocket Range.
Hunter and U.S. astronaut Col. Benedict watch the successful firing of the Prometheus anti-missile weapon. Hunter is assigned to protect Benedict on his Australian goodwill tour; Kragg and Smith plot to kidnap the astronaut, who, on his return to the U.S., is to lead a four-man space probe, which the CUCW plan to sabotage.
After kidnapping Col. Benedict, the CUCW deceives a student group, the Australian Student Protest, into hiding him. Hunter traces Benedict to Melbourne's outer suburbs, and finds Kragg, disguised as a left-wing journalist, attempting to murder Benedict in a car accident.
Hunter saves Colonel Benedict's life after Kragg has abandoned him in a van careering down a hillside. Hunter meets members of the Australian Student Protest whose lives are threatened because of CUCW reaction.
Kragg deceives Australian Student Protest member Jamie Porter into believing that Australian and U.S. security agents arranged the murder of his friend Kelly, and that he is next on the list. Porter, an excellent marksman, is taken to a hideaway, given a serum and mentally conditioned to carry out the death by sniping of Col. Benedict during a city street procession.
Student Jamie Porter is drugged and goaded into assassinating Col. Benedict as he drives through Melbourne's streets in the Moomba procession. Hunter intercepts Porter on top of a building overlooking the corner of Swanston and Collins Streets.
Hunter, disguised as a Navy commander, and Eve go to Singapore, where a major disarmament conference is to be held between western powers and Russia. The CUCW intend to sabotage the conference by murdering Russian advance agent Gregori Loschenko and blaming British agents.
Russian agents kidnap Eve, believing British and Australian agents kidnapped Loschenko. Hunter traces Loschenko to a sampan on Singapore Harbour, where he is held captive by the CUCW. The boat explodes with Loschenko drugged aboard it.
Kragg murders Andrea, a girl employed by the Russian Embassy, who had been giving information to the CUCW for sabotaging the peace conference. Hunter has his first face to face encounter with Kragg when they fight on an aircraft preparing for take-off.