While haggling with a pair of twinned Miradorns over a valuable goblet for which he had agreed to provide a buyer — until learning that the artifact in question may have been acquired illegally — Quark is interrupted by a newly-arrived alien from the Gamma Quadrant named Croden, who bursts in on the meeting brandishing a phaser and demanding the goblet for himself. A battle erupts, and Croden ends up killing one of the twins. Odo, who observed the exchange in disguise after becoming suspicious, morphs back into humanoid form and breaks up the fight, taking Croden into custody and ordering the others to meet with him and Sisko. The surviving twin, Ah-Kel, makes it clear that he is determined to get revenge by killing Croden. Meanwhile, Croden, in a holding cell, shows little remorse, and little interest in anything but food. However, he manages to mention during a conversation with Odo that he has encountered other "Changelings," or shape-shifters, in the Gamma Quadrant. Odo is suspicious, but intrigued.
Sisko decides the best course of action is for he and Dax to locate Croden's home planet of Rakhar and notify the authorities while increasing security to protect him from Ah-Kel. Odo, already suspecting that Croden staged the attempted "robbery" with Quark, tries to learn more about Croden's origins from the Ferengi. Later, Croden tries to appeal to Odo, offering to take him to a place where other Changelings may still live, but Odo is still distrustful. Croden then gives him a locket containing an odd stone that morphs into an intricate metallic object and back to its original shape. He tells Odo the stone is from the colony of changelings.
Dax and Sisko make contact with Rakhari officials, who call Croden a criminal and an "enemy of the people" and demand his immediate return. Meanwhile, Odo takes the stone to Bashir, who analyzes it and determines that it is an amalgam of organic material and some sort of crystal, and that the only life form bearing even a passing resemblance in structure is Odo. Unable to help being fascinated, Odo breaks down and asks Croden where he got the stone. Croden says it came from an asteroid in the Chamra Vortex, on the other side of the wormhole. Claiming that he chanced upon a changeling colony on this uncharted asteroid, Croden offers to take Odo into the dangerous, uncharted territory. But Odo still cannot trust Croden, and does not respond to his offer. Sisko, after returning from Rakhar, tells Odo to escort the prisoner home. Odo and Croden board a Runabout and set a course through the wormhole for the planet, escaping the detection of Ah-Kel, who still wants Croden for himself.
En route to what he knows will be his doom, Croden again tries to win Odo's trust, explaining that he was also an outsider on his own planet and that the Rakharis killed his family. Back on the space station, Ah-Kel threatens Quark, who directs Ah-Kel toward Odo and Croden rather than risk getting caught for his own part in the Miradorn's death. Now in pursuit, Ah-Kel attacks Odo's ship, but Odo refuses to surrender his prisoner despite the fact that he cannot outrun Ah-Kel. With no other choice, he lets Croden pilot the ship through the Vortex, where the ionized gasses will hide them from Ah-Kel's sensors. To Odo's surprise, Croden lands the Runabout on the asteroid where the shape-shifters supposedly live.
Croden anxiously rushes into a cave, almost losing Odo, who angrily demands to know what is really going on. Croden finally admits the truth — the morphing stone is actually a key to a stasis chamber, inside of which is his peacefully-sleeping daughter, the only member of his family he could save when the Rakhari forces attacked them. He introduces Odo to the girl, Yareth, and tells her Odo will take her to a safe place while Croden will return to face the authorities on Rakhar. Suddenly, an explosion rocks the cave. Odo is knocked unconscious, but rather than using the moment to escape, Croden carries him back to the ship, saving his life. Odo regains consciousness back on the Runabout, with Ah-Kel's ship still in pursuit. He takes control and is able to trick Ah-Kel into destroying his own ship before leaving the Chamra Vortex for good. Once outside, Odo surprises Croden by having the alien and his daughter transported aboard a Vulcan ship, protecting them both from imprisonment or death on Rakhar. In exchange for his kindness, Croden gives Odo the changeling stone, a reminder that other shapeshifters may really exist out there somewhere.