DS9 Season 2 Episode 12 The Alternate

Plot

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. Commander Sisko refers to his own father here in the past tense yet Sisko senior later plays a role in the series.
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.
Bashir is studying the remains in the infirmary when he is attacked by a strange creature, which he fends off with a laser scalpel. Dax's analysis of a sample reveals the DNA of the life form and the creature are different, and begins a computer search for a match with known life forms. Mora, meanwhile, recognizes the DNA pattern as Odo's and confronts him privately. He points out that the attacks occurred approximately sixteen hours apart, exactly the times when Odo reverts to his natural gelatinous state to regenerate. They surmise that the gas on the Gamma Quadrant planet might have affected Odo somehow. Panicking, Odo begins to head for the infirmary, but Mora claims Bashir will not understand and will treat Odo like a monster. He presses Odo to come back to Bajor with him, and, as he does so, the increasingly agitated Odo again transforms into the creature.
Security picks up a power drain in Odo's office, but, when they arrive to investigate, they find nothing amiss. Having seen Odo's violent reaction to him, Mora explains to Commander Sisko and Major Kira that he is the cause of Odo's metamorphosis. The first time, he explains, the creature was trying to rescue the organism Mora had contained in the science lab; the second time, it appeared in the infirmary, where Mora was a patient; and the third time, Odo and Mora were in the middle of a heated debate. He helps the crew lure Odo in his altered state to the Promenade, where he is contained in a force field and reverts to normal.
Later, the effects of the gas having been removed, Odo apologizes to Mora for attacking him. Mora apologizes to Odo for ignoring his feelings, which he finally realizes what he had done when Odo had felt like a prisoner in his laboratory. Mora says he would like to be a part, however small, of Odo's life, and the two begin to reconcile.