Dr. Mora Pol, the Bajoran scientist who studied Odo when he was first discovered, arrives on Deep Space Nine and tells Odo that he has picked up DNA signatures similar to Odo's on a planet in the Gamma Quadrant. Mora, Odo, Dax, and Mora's assistant depart for the planet in a runabout to investigate, and while en route, Mora's fatherly attitude toward Odo, including embarrassing stories from their early time together, irritate him.

Upon reaching the planet, the four of them beam to the surface, where they discover a tiny life form that may be a distant relative of Odo. Before they can return to the runabout, however, an earthquake releases volcanic gases into the air. The other three pass out, but Odo, unaffected because he does not have a respiratory system, beams them back to the runabout.

Back on the station, Dax and the others are brought to the infirmary to recover, while the life form is brought to the science lab, where O'Brien tries unsuccessfully to identify it. As it appears to be growing, he puts it into a containment field, but later that night, the crew finds the lab damaged, and the life form gone, apparently having escaped through an air duct. They note that the incident was accompanied by a power drain and a rise in temperature. O'Brien, attempting to track the creature down, hears a strange noise, and then finds a puddle of goo, which they assume is the life form's remains.

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