Stardust City Rag

Years ago, Seven of Nine was forced to euthanize her adopted son, Icheb, after his Borg implants were ripped out by black market dealer Bjayzl. Now, Seven travels with La Sirena to Freecloud, where Raffi learns that Bjayzl has Maddox captive and intends to sell him to the Romulans. To free Maddox, Picard's crew stage a prisoner exchange with Seven as the bait. Meanwhile, Raffi unsuccessfully tries to reconnect with her estranged son Gabriel before returning to La Sirena. When Bjayzl recognizes Seven, the latter drops the charade and reveals her true intention: to kill Bjayzl and avenge Icheb. Picard convinces Seven not to seek revenge, and Maddox is safely beamed to La Sirena. Later, Seven returns to Freecloud and kills Bjayzl without Picard's knowledge.

Summary from Wikipedia, CC BY-SA 4.0.