Tey'sa was a young female member of a subterranean civilization on an unnamed planet, which had become dependent on the power of the crashed wreckage of a Borg cube. When the crew of the USS da Vinci discovered this society in 2377, Tey'sa was the first to approach the newcomers. She brought the Federation team, including Commander Sonya Gomez and Lieutenant Commander Domenica Corsi, to "meet" their leader, the Sage, and then provided a tour of the entire settlement.

During the crew's visit, the Sage died, and Gomez was unwillingly attached to the alcove in a manner akin to assimilation, becoming the new Sage. Fortunately, the S.C.E. team was able to free her, and once they had, Corsi convinced Tey'sa to take her place as Sage. (CoE eBook: The Light)