A Boslic Captain talks Quark into purchasing the wreckage of a ship that crashed in the Gamma Quadrant. Unfortunately, he ends up with much more than he bargained for when he finds a newborn alien infant hidden inside. Quark brings the baby to the Infirmary, where the child's presence reminds Sisko of his teenaged son Jake's own infancy — and Sisko's fatherly concern now that Jake is dating Mardah, a 20-year-old Dabo girl. Bashir notices that the baby has a phenomenal metabolic rate, and the child develops so rapidly that he changes from an infant to what looks like an eight-year-old boy in a few hours.
While the boy is no more than two weeks old genetically, he is already able to speak. Bashir soon determines that his advanced skills are artificially implanted as the result of genetic engineering. The crew quickly sees what kind of alien he is when the boy matures again — into a violent, teenaged Jem'Hadar.
Sisko plans to send the teenager to Starfleet Command for study, but Odo objects, knowing what it is like to live as a lab specimen. Despite the danger the Jem'Hadar poses, Odo wants to prove that he isn't just a programmed killing machine. He asks Sisko to let the boy stay, thinking he can control the alien since Jem'Hadar soldiers are bred to serve Odo's race of shapeshifters. Because the child's race is dangerous to the Federation, Sisko is reluctant, but he lets Odo work with the boy. Later, Mardah joins Sisko and a nervous Jake for dinner. But, despite his initial thoughts, Sisko finds Mardah to be very nice — and learns some things about Jake in the process. Meanwhile, Odo talks to the alien, who shows his obedience, then expresses a desire to stay in Odo's quarters, which he allows.
Odo talks at length with the teenager, and learns that he wants to know more about the Jem'Hadar. But the boy's only desire seems to be for violence. Kira warns him that the child may be a lost cause — if he was engineered to kill, Odo will not be able to change him. Odo tries to show the teenager that there is more to life than fighting, but a holosuite battle reveals that the bloodlust remains. Later, Sisko has word that Starfleet has sent a ship to pick up the young Jem'Hadar. But before Odo can leave to tell the boy, he suddenly appears in the room, pulls a phaser on Sisko, and announces that he refuses to go where they plan to send him.
The teenager demands a Runabout so he and Odo can go home to the Gamma Quadrant, then takes him through the corridors en route for the vessel. Much to Odo's disappointment, the boy reveals that he wants to be a Jem'Hadar. But when Sisko attempts to stop him from leaving, Odo intercedes, insisting on returning the teenager to his homeland. Knowing that the Jem'Hadar will either kill someone or be killed rather than go with Starfleet, Sisko agrees. Odo handles this final task and returns to the station, sadder but wiser for his experience.