Bat Costovan, a seasoned and hard-built prize-fighter, meets Mame Harmer, a professional strong woman, who impresses him with her combination of strength and beauty. Despite her muscular prowess, Mame retains a feminine grace that distinguishes her from the typical strong women Bat has encountered. They engage in a conversation about strength and fighting styles, with Mame explaining her training in Japanese jiu-jitsu, which maintains her symmetry and femininity.

The conversation shifts to Bat’s upcoming fight with Romaro, an Ecuadorian fighter. Despite his reputation and experience, Bat confides in Mame that he is planning to throw the fight. He explains that the gambling ring has orchestrated the match to position Romaro for a title bout. Bat reveals his weariness with the sport and his realization that he is getting too old to compete with younger fighters like Kid Hurley.

Mame, deeply concerned, reveals that her younger brother, an avid boxing fan, has bet ten thousand dollars of the bank’s money on Bat to win. Despite her pleas, Bat insists he cannot back out of the fixed fight without facing severe consequences from the gambling ring.

In a desperate move to save her brother from financial ruin, Mame uses her jiu-jitsu skills to break Bat's wrist, rendering him unable to fight. Despite the pain, Bat understands her motivation and admires her resolve. He acknowledges that she has successfully prevented him from participating in the fight, thus avoiding the fixed outcome.

In the aftermath of the confrontation, Bat proposes marriage to Mame, suggesting that their combined strength and resilience would produce exceptional children. Mame agrees, and they leave together to have Bat's arm treated, contemplating a future together.

"Thoroughbreds" blends themes of honor, integrity, and romance within the gritty backdrop of the boxing world, culminating in a resolution that emphasizes personal values over professional obligations.