Carter is shown a box containing the shriveled genitals of a man – the only remains of a CIA agent investigating a communist pornography ring based in Budapest, Hungary.
Several of the films feature Mona Manning – a former Hollywood actress forced into making pornography due to her waning career and poor mental health.
Carter is ordered to infiltrate the pornography ring and targets Paulus Werner – a West German national who recruits young women from the UK and Western Europe for the pornographers under the cover of a travelling theatrical troupe.
Werner identifies Bela Kojak as his contact in Budapest and reveals that the entire pornography ring is organized by the mysterious Dr Miljas Eros with the involvement of Chinese diplomat, Fang Chi.
At their hotel, Carter discovers a stash of heroin hidden in the theatrical troupe's equipment and suspects Paulus Werner of operating a clandestine drug smuggling ring.
In Pest, Carter hires a small boat to take him up the Danube to Vác, where Michael Blackstone lives in a villa.
Before he can free the captive women Carter eavesdrops on a high-level meeting between Blackstone, his wife, Bela Kojak, Fang Chi and Mona Manning.
Carter is captured, stripped, shackled to the floor and subjected to peine forte et dure – crushed under heavy stones.
Kojak believes him to be a superior American agent and surmises he is indeed Nick Carter and debates whether to sell him to Russian or to Chinese authorities.
Carter and Pamela tie themselves together and dive overboard, negotiating the underwater nets that prevent unauthorized entry and exit into Hungary.