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He is the first scientist selected to be contacted by Captain Troy and Lieutenant Dillon in their mission of making contact with the scientists of Earth, given his work on nuclear power. In particular, Mortinson was working on an abstract theory of nuclear degeneration since roughly 1977, according to Dorothy Carlyle. He also worked on various papers, including one on brother worlds and atomic travel, which Troy and Dillon references in their conversation with Carlyle.
Mortinson is convinced of their being from a different planet after they leave a completed mathematical formula on his computer. He arranges a meeting with the two Colonials, but recognizes that Jamie Hamilton is trying to capture him on film and they escape.
Despite his aversion for the media, he later does an interview with Mr. Brooks at the United Broadcasting Company, attempting to convince people that the "two young men" were not terrorists, which fails. After the interview, he is approached by Xaviar, who he later brings back to his large beach house. It is here where Xaviar attempts to convince him that Troy and Dillon are outcasts, in addition to a vain attempt to convince him of the benefits of altering Earth's history in order to speed up the development of technology. This fails when Hamilton calls him and attempts to warn him of Xaviar, who disconnects the phone and stuns him.
Later, he is apparently contacted by the Air Force Colonel, who brings him to Van Nuys A.N.G. Base to help explain the technology of the Vipers they had temporarily captured. Mortinson assures them that the craft were not of Russian origin, but of an extraterrestrial one (Galactica Discovers Earth, Part III).
He is later mentioned as monitoring Colonial frequencies for Dillon and Troy, although as he does so he is unable to detect the Cylon frequencies emitted by the A-B Raider (The Night the Cylons Landed, Part I).