Ghost Dog, a man who perceives himself as a retainer to a local mobster, Louie, finds his life intertwined with the code of the samurai after Louie saved him years ago. Living as a hitman within the American Mafia, he adheres to the ancient wisdom of the Hagakure.
When Louie tasks Ghost Dog with eliminating a gangster named Handsome Frank, who is involved with the daughter of mafia boss Vargo, Ghost Dog follows through meticulously. He successfully kills Frank but chooses to spare the girl, leaving her unharmed despite the circumstances. In the aftermath, Vargo and his associate, Sonny Valerio, conspire to eliminate Ghost Dog to distance themselves from the made man's murder. Unfortunately for Ghost Dog, Louie remains mostly oblivious to the hitman's life, as Ghost Dog communicates solely through his homing pigeons. Determined to find Ghost Dog, the mobsters begin tracking pigeon coops, eventually discovering Ghost Dog's covert abode and killing his beloved birds. Realizing the peril he’s in, Ghost Dog understands he must take out Vargo and his men before they turn on him and his loyal master.
Throughout his day, Ghost Dog often visits a park to see his closest companion, Raymond, a French-speaking ice cream vendor. Their lack of a shared language—Raymond speaks French while Ghost Dog speaks English—doesn't hinder their unusual but profound connection. Ghost Dog also befriends a young girl, Pearline, entrusting her with a copy of Rashōmon.
In a spectacular turn of events, Ghost Dog invades Vargo's mansion, single-handedly dispatching nearly all of Vargo's men but sparing both Louie and Vargo's daughter out of respect. As night falls, he strategically ambushes Sonny Valerio in his home, shooting him. Perceiving that Louie might feel bound to retaliate for Vargo's death, Ghost Dog visits the park to provide Raymond, who struggles to survive in the country, with all his money. Pearline reappears and returns the book Rashōmon, expressing her enjoyment of it. Ghost Dog gifts her his own copy of Hagakure, encouraging her to delve into its pages.
Despite his loyalty to Ghost Dog, Louie ultimately confronts him at Raymond's ice cream stand, where both Raymond and Pearline bear witness to their exchange. Ghost Dog, however, finds himself unable to harm his mentor, allowing Louie to strike him down. In his final moments, he offers Louie the copy of Rashōmon with a suggestion to read it. Pearline takes notice, directing Ghost Dog's empty firearm toward Louie as he retreats. In the end, Ghost Dog meets his peaceful demise flanked by Raymond and Pearline, while Louie drives away with Vargo's daughter, who has assumed her father's role in the criminal hierarchy. In a poignant finale, Pearline immerses herself in the teachings of the Hagakure.
