While listening to a complaint about Quark's lascivious behavior from a Dabo girl, Sisko is alerted that an alien vessel is coming through the wormhole. The vessel contains a reptilian being named Tosk, who reluctantly agrees to allow O'Brien to tow in his destroyed ship.
O'Brien then boards Tosk's ship to inspect its systems and introduce himself. Though suspicious of O'Brien's kindness, Tosk follows him onto the Promenade and is fascinated by all that he sees. After talking awhile, O'Brien learns that Tosk is very different from human beings — he requires very little sleep, food, and he has no sense of humor. His behavior seems odd to O'Brien, and he alerts Sisko to keep an eye on him.
After talking more with Tosk while repairing his ship, O'Brien tells the rest of the officers that he thinks Tosk is in danger. Then, Odo discovers Tosk altering a junction box in a remote corridor and apprehends him. Much to Sisko's frustration, Tosk does not respond to questioning, and O'Brien feels partially to blame for the mess because he introduced Tosk to the station.
Later, a new ship with emission patterns that match those of Tosk's ship arrives at Deep Space Nine, and three aliens beam aboard without invitation. The beings are hostile, and a phaser battle ensues as they are able to enter Odo's security office and capture Tosk.
The lead alien then informs Sisko that he is a hunter and Tosk is his prey. Sisko tells the hunter that his type of blood sport is no longer practiced at this station. Against his better judgment but in accordance with Starfleet's Prime Directive, Sisko agrees to release Tosk into the hunter's custody. Then Kira, sensitive to O'Brien's feelings of despair for his new friend, suggests that Tosk request asylum — thus allowing him to be protected by the Federation.
Alas, Tosk refuses to go against his culture and does not ask for asylum. However, O'Brien, claiming to have orders from Sisko, intervenes when the Hunter tries to take Tosk off the station. O'Brien programs a security checkpoint to debilitate the Hunter as they pass through it, and he grabs Tosk and leads him to a narrow escape.
Sisko reprimands O'Brien for taking matters into his own hands, yet it is obvious that Sisko thought he did the right thing. Killing, they agree, simply for the sake of sport should not be allowed in any star system.