Set in the 24th century, the series follows the adventures on Deep Space Nine, a space station located near a stable wormhole between the Alpha and Gamma quadrants of the Milky Way Galaxy. The plot of "Rejoined" expands on the Trill species, of which DS9 officer Jadzia Dax is a member. They are formed of a host and a symbiont, with the symbiont passed from host to host as the previous one dies. In the episode, Dax is reunited with Lenara Kahn, the widow of one of the symbiont's former hosts. The two struggle with their feelings for one another because of the taboo in their species against reuniting with loved ones of former hosts as they work together to experiment on wormholes.