In that year, he was involved in a conspiracy to sabotage peace talks between the Federation and the Klingon Empire. While in a meeting with the Federation President after the arrest of James Kirk and Leonard McCoy, Nanclus lent his support to "Operation Retrieve," the proposal to infiltrate Klingon space and rescue the hostages, put forth by Nanclus' fellow conspirator, Colonel West. Later, Nanclus attended the Khitomer Conference. After the crew of the USS Enterprise-A learned of his involvement in the conspiracy, and successfully prevented the assassination of the Federation President at the conference, he was detained by Starfleet. (Star Trek VI: The Undiscovered Country)
The non-canon novel Sarek indicates that Nanclus suggested the conspiracy to Admiral Cartwright and General Chang.
In the non-canon novel Cast No Shadow, "Nanclus" is said to be a Tal Shiar operative who used that name and the role of an ambassador as a cover. When the conspiracy was uncovered, "Nanclus" was recalled to Romulus, where the official report was that he was executed by disintegration. In reality, though "Nanclus" was given a different identity and assignment. In 2300, he was involved in a failed attempt to support Kriosian terrorists in rebelling against the Klingon Empire. After the plan failed, "Nanclus" and the other Tal Shiar chiefs were killed by by a Klingon agent named Kaj.