In the live-action film adaptation, the familiar story is transplanted from Victorian England to a fictional, futuristic 2020 metropolis, a strange fusion of Eastern and Western cultures. The narrative follows Shiori Genpo, a young woman who has secretly assumed the identity of the heir to the Phantomhive family. Because only males can inherit the position of family head, she disguises herself as a man to uphold her family's noble legacy and continue their secret work as the Queen's Watchdog, investigating crimes and disturbances in the underworld. The central conflict arises from a supernatural contract she has forged with a demonic butler named Sebastian Michaelis. Bound by this pact, Sebastian must protect and serve Shiori with his superhuman abilities, assisting her in a mission of vengeance against those who wronged her family. The terms of their dark bargain are absolute: Sebastian will help her hunt down her parents' killers, and once their revenge is complete, he will be permitted to consume her soul.

The live-action film departs significantly from the source material not only in setting but also in its core characters. While the original manga features the young earl Ciel Phantomhive, the movie introduces Shiori as a descendant of the Phantomhive line. Her personal quest for vengeance is complicated by a society that bars women from leadership, forcing her to conceal her true identity. Sebastian remains the impeccable, ruthless, and nearly invincible demon butler, played by Hiro Mizushima, who is both her most faithful servant and the one destined to claim her soul.

The narrative arc unfolds in this alternate reality as Shiori and Sebastian delve into a mystery involving an illegal and experimental drug that is terrorizing the city. The plot revolves around uncovering the source of this deadly substance and the shadowy organization behind it, which is linked to the tragedy of Shiori's past. Unlike the episodic mystery format of the anime, the live-action film presents a self-contained story focused on this specific criminal conspiracy. The butler's supernatural powers are put on display as he protects his master and eliminates obstacles with brutal efficiency, all while the countdown to their contract's completion continues.