In a fictional ancient Rome, an unnamed gladiator fights against tigers, buffaloes, bears, elephants, antelopes and even monitor lizards in the circus arena, but also against men. He fights with three other gladiators, Cleophas (Terry Notary), Eolus (Matt Cipro) and the trembling and mentally disturbed Cleisthenes (Liang Yang), occasionally against them.
The youngest daughter, Livia (Dafne Keen) of the emperor Pyrrhus (Riccardo Scamarcio) is madly in love with him. Watching the arena's fights only to see the gladiator. As the fight with the monitor lizards ended, Cleophas asked Cleisthenes to finish off a fallen gladiator. Cleisthenes, raising his head abruptly without a word, complied by opening the throat of their fallen brother-in-arms with a sharp blow. The gladiator exchanges a dry look with Cleophas, and without a word returns to the locker room while the others clean the arena. After the fight, after the sand has settled and the surrounding fury has subsided, Livia slips into the locker room now occupied only by the gladiator dear to her heart. As she enters the gladiator exchanges only a brief look of amazement, but she silences him and begins to undress him.
The emperor is of course unaware of the fact that after the brawl, his daughter met the gladiator in person in the locker room and had an passionate affair with him began.
The empress, Valeria (Gemma Chan) does not like her husband, her violent and vindictive attitude is more and more unbearable and his sexual behavior is even worse. She has a brief interview with Marcus, one of Nero's top generals, and hatches a plan with him to get rid of Pyrrhus. She lets Marcus know that the rebellion already has a plan and that there is no point in him risking his life at this point. Valeria lives a real and touching love story with the poet and philosopher Flavius (Louis Garrel), she also plots in the shadows with one of the latter's military leader centurion Marcus (Colin Woodell) to assassinate him. Flavius is also part of a small rebellion movement planning a decisive blow soon.
Livia cannot hide the truth any longer from her older sister, Octavia (Monica Barbaro) who, compassionate, reveals nothing while making remarks on how risky her situation was. Octavia later finds the court hunchback, Quintus (Sebastian Hülk), in a dark area of the hall, seeing him in emotional distress, she takes a seat next to him, not frightened by his appearance, or hiding it well, and takes time to speak to him kindly.
But the second sister, Julia (Isabela Merced), the beautiful but as cruel as her father, reveals everything to the Emperor. Who decides after an interview with one of his advisors, Lucius (Billy Zane) to kill him unofficially in the arena, by making him fighting the best gladiator and the gladiator's mentor (Aaron Moten), and locked Livia in her chamber as a punishment, Quintus witnessed the imprisonment. But the advisor is aware of the brutal and irrational direction Pyrrhus's policy is taking, and plot with the insurgents that Flavius belonging to start fire into the palace, not having foreseen that Pyrrhus would lock Livia up to punish her for her affair with the gladiator, and that he would force the latter, that same evening, to fight his mentor in the arena. Lucius, Flavius and Aurelia (Kelly Hu) Lucius' wife, develop the plan for the resistance, while Flavius leaves the place, Aurelia takes the time to tell her husband that he risks a lot by giving him a neck massage, but he being convinced of the need to bring down Pyrrhus does not cancel the plan.
The next morning, the gladiator and his mentor entered the arena. After a long duel, the brawl ends with the mentor's suicide, and a false victory for the gladiator. Octavia realizes that Livia is locked up, and, going against her father's orders, tells Quintus to go get the gladiator before Pyrrhus while she herself takes care of Livia. In several places in the city, torchbearers begin to light the fire while several many insurgents dispose of the guards. Livia, frightened, locked in her room thinking of the gladiator risking his life in the arena, she tries in vain to escape but she later succeeds thanks to Octavia who forced the lock. Right after the duel, while the mentor's body is not even cold yet, Cleophas, Eolus and Cleisthenes enter the arena, all three driven by revenge or jealousy towards the gladiator. The gladiator killed Eolus by slitting his throat and later Cleisthenes by planting his own sword in his right eye. He willingly spares Cleophas after disarming him, but he does not surrender and the gladiator is forced to finish him off.
After the fight the gladiator is back in the locker room, and Quintus, wanting to get ahead of Pyrrhus, visits him, which scares the gladiator, but after a cynical remark against Quintus, the gladiator realizes that he is there to help him.
As fire breaks out and begins to devour the city, people flee, chaos reigns, Quintus and the gladiator leaves the arena and runs to find Livia. Valeria finds Flavius and flees the city with him. As the fire spread through the city and the palace. In the palace, a violent gust of wind detaches the flaming curtains which burns Julia alive. Octavia dies by accident while trying to escape from the palace with Livia, the gladiator and Quintus, the ground giving way under her feet, she falls directly into the fire. The emperor sees his daughter and the gladiator together draws his sword but Quintus and Marcus who had conspired against him with Valeria intervenes. Quintus is mortally wounded and after a look at the gladiator and Livia, collapse on the ground without a single word. After a long duel, Marcus deliver a blow directly to the heart of Pyrrhus.
Livia and the gladiator flees to another room but find themselves trapped by the flames and embrace as the ceiling collapses on them. Final fate of Marcus is unknown. The story ends with Valeria and Flavius watching the city in fire and blood in the distance, fleeing in the early morning.