Shen Kuei is a man based in Hong Kong who dealt in espionage and counterespionage and who became known as Cat because of his cunning, stealth, and mysteriousness. At on time he worked for the People's Republic of China.
Sir Denis Nayland Smith, an agent of the British intelligence agency MI-6, asked his ally, the martial arts master Shang-Chi, to go to Hong Kong to stop Cat's operations and to recover certain documents from him that had been stolen from British intelligence. Smith warned Shang-Chi that the life of a British counterpart was in danger from Cat. Shang-Chi accepted the mission.
However, Smith was unaware both that Cat had left the employ of the Communist Chinese and that the British counteragent, a woman named Juliette, had fallen in love with Cat. Juliette told Shang-Chi where to find the documents but said she wanted to stay in Hong Kong with Cat. Shen Kuei, however, wrongly believed that Juliette had betrayed him to Shang-Chi and that Shang-Chi had been sent to assassinate him. Enraged, Cat intended to kill them both. Shang-Chi obtained the paper that Smith wanted, only to be told by the man he took them from that they were not stolen from the British after all. Believing him, the disillusioned Shang-Chi threw the papers away. However, the papers did indeed belong to British intelligence and described the activities of Shang-Chi's father, Fu Manchu, a major threat to the world's security. Cat and Shang-Chi, both consummate masters of the martial arts, battled each other until Juliette, to stop the fight, plunged a knife into shoulder. Horror struck and guilt-ridden, Cat broke off the fight and went to Juliette, begging her forgiveness. He threw a knife to Shang-Chi, giving him the opportunity to kill him. But Shang-Chi spared Cat's life and returned to London.
Shen Kuei and the master criminal Kogar became partners to obtain the plans for a neutron bomb. But then the partnership ended, and Shen Kuei, again working for the Communist Chinese, acquired the plans for them. The relationship between Juliette and Shen Kuei had ended: she felt his love for her had lessened, and she believed his current work for the Communist Chinese was "evil" although she did not know exactly what he was doing for them. Finally, Shen Kuei had taken a new lover, the mercenary Pavane; Juliette herself fell in love with another mercenary, Skull-Crusher. Juliette decided to help Kogar hijack the barrels containing microdots with the bomb plans from Shen Kuei's men. However, Kogar tricked her into leaving a barrel containing explosives which killed Shen Kuei's brother, the owner of the Jade Peacock, a Hong Kong nightclub.
Eventually, Cat and Shang-Chi both arrived at Kogar's secret base. There Cat accused Kogar of treachery and demanded a trial by combat. Kogar chose Shang-Chi, who had just infiltrated Kogar's organization, to act as his champion. Hence Cat and Shang-Chi again met in combat, but during the fight, Cat learned that it was Kogar, not Shang-Chi, who was responsible for his brother's death, and broke off the duel. Shang-Chi destroyed the plans for the neutron bomb, and he and Cat joined forces to destroy Kogar's base with explosives.
Cat decided to work no longer for any governments. He learned of a German ship that sank off Hong Kong during World War II and that it contained research papers and canisters of a rare substance, both of which would make possible the construction of an effective long-range particle beam weapon. Cat decided to obtain the papers and canisters and to destroy them before any government could make use of them. Shang-Chi's lover, Leiko Wu, was sent by MI-6 to obtain the papers and canisters, but she began an affair with Cat and chose to aid him in destroying the information and canisters. Shang-Chi agreed with Cat's goal once he learned of it. Cat recovered the papers and canisters from the German ship, destroyed the papers, and buried the canisters. He confessed to Wu that he was still in love with Juliette, who now worked for him, and Wu told him she still loved Shang-Chi. Not realizing that Shang-Chi sympathized with his destruction of the particle beam secret, Cat battled him, but their fight ended when Leiko and Juliette aimed guns at each other, threatening to fire them if the battle continued. Leiko returned to Shang-Chi and Juliette returned to Cat. Cat had the German ship destroyed. Chen Kuei and Shang-Chi parted as respectful allies.