The film opens as a well dressed, barrel chested man stalks the late-night passengers of a subway train. He assaults and kills several people with a meat hammer, and a butchers hook. He dispatches his prey wordlessly, and with an uncannily unnatural strength. He wears a ring on his finger, adorned with eight stars.We are then introduced to Leon, a vegan photographer who heads into the city's subway system at night to take photographs. He is criticized constantly by other photographers for fleeing danger before shooting a full reel. One night, in a decision to break this trend, he saves a woman from a gang that is abusing her. The next day, he discovers this girl has gone missing. Leon is intrigued by the mystery, and begins to investigate newsreels about similar disappearances. His investigation leads him to a butcher named Mahogany, who he suspects has been killing subway passengers for as long as a hundred years.Leon attempts to turn some of the photos he has taken of Mahogany in to the police, but they refuse to believe him, and instead cast suspicion on his own motives in photographing the victims. Leon's involvement quickly turns into a dark obsession, upsetting his waitress girlfriend Maya, who is as disbelieving of his story as the police chief. Leon takes matters into his own hands, entering the subway train at midnight, only to witness a shocking bloodbath, as the butcher kills several passengers, then hangs them on meat hooks. Passing out on the subway floor, he awakes the next morning in a slaughterhouse with strange markings carved into his chest.A concerned Maya and her friend Jurgis, a short-order cook, begin to examine the photos Leon has been taking of Mahogany, leading them to the killer's apartment. After breaking and entering the butcher's home, Jurgis is captured, and brutally killed. Maya goes to the police, But finds that they are as unwilling to consider her story, as they were of Leon's. It is at this point that we begin to discover that the police may be involved in the cover-up of Mahogany's crimes. A police official directs the misguided Maya to a trip on the midnight train. Leon, unaware of Maya's involvement, finally decides to put an end to the butcher's crimes, and heads to the hidden subway entrance in the slaughterhouse, arming himself with the a butcher's apron, and several slaughterhouse knives.Leon enters the train as Mahogany has completed his nightly massacre, and has cornered a helpless Maya. Leon attacks the murderer with a knife, beginning a climactic battle between the photographer and the superhuman butcher. They fight in between the swinging human meat, Leon's knives against Mahogany's meat hammer, and human body parts are ripped, thrown, and used as weapons in the shower of epic gore. Finally, Mahogany is thrown out of the train by Leon, but not long before it hits its final stop. The train has entered an underground cavern, filled with skulls and decomposing bodies. Mahogany, in a battered and bleeding state, returns, barely alive, from beneath the train, and engages in a death struggle with Leon, who finishes the job at last by impaling the psychotic butcher's skull on a blade. Mahogany grins in his dying throes, pronouncing the single word "Welcome!"With the butcher's death, the conductor of the train enters the car, advising Leon and Maya to "Please step away from the meat." With these words, the true purpose of the underground station is revealed, as horrible reptilian creatures enter the car, consuming the meat to which they have been delivered. The conductor explains to Leon that the creatures have always existed below the city, and that the butcher's job was to keep them satisfied by feeding them every night. The conductor then forces Leon to watch as he kills Maya with one of the butcher's knives. When he is done, he picks up Leon, and with the same supernatural strength as the deceased butcher, rips out Leon's tongue, throwing him to the ground. He tells Leon that, having killed the butcher, he must take his place.In the final scene, the police chief hands the train schedule to the new butcher, who wears a ring with eight stars. The killer walks onto the midnight train, and turns his head to reveal that he is Leon, ready to go on his nightly slaughter.
Output: Question: What is Leon investigating?, Answer: A missing girl