A Trill outcast takes the station hostage to steal Dax's symbiont.
During a plasma storm, with the station down to a skeleton crew, the unjoined Trill Verad boards with two Klingon mercenaries and his companion Mareel, helped by Quark. Verad was once rejected for joining, and he forces Bashir to move the Dax symbiont from Jadzia into him, leaving Jadzia only hours to live.
With the symbiont, Verad has the memories of Curzon, Sisko's old mentor, and Sisko tries to reach that part of him. Bashir and Quark work against the mercenaries, Odo is freed, and Mareel finally turns against Verad. Sisko stuns Verad before he can escape, and the symbiont is returned to Jadzia.