Frank Leone, played by Sylvester Stallone, is a talented mechanic and former football player living in Hoboken, New Jersey. Nearing the end of his sentence at a low-security prison in Norwood, he enjoys occasional outings to fix cars in his garage, reminiscing about his childhood and the memories shared with his late father. He cherishes moments with his girlfriend Melissa, who often drives him back to prison and gifts him a lucky charm necklace to keep his spirits high.
However, one fateful night, as he sleeps in his cell, guards unexpectedly drag him to the grim maximum-security facility called Gateway Prison, ruled by the tyrannical Warden Drumgoole. Unbeknownst to many, Leone has an unresolved history with Drumgoole - the man who oversaw his previous incarceration at Treadmore, where Leone was the only inmate to successfully escape. His flight was motivated by a desperate need to see his dying mentor, a request denied by Drumgoole. Therefore, driven by justice, Leone had previously exposed the inhumane treatment of inmates, forcing the warden's transfer to Gateway.
Inside Gateway, Leone forms bonds with fellow inmates: Dallas, Eclipse, and First-Base. Together, they work on restoring a Ford Mustang, lovingly named "Maybelline." When First-Base brazenly starts the engine, chaos erupts as the car crashes out of the garage, resulting in Leone facing the wrath of Drumgoole, who punishes him by sending him to solitary confinement for six long weeks.
In a cruel twist, the warden manipulates events to justify additional punishment, allowing violent inmates like Chink Weber and his gang to attack Leone in the gym. Despite defeating Chink, Leone's act of mercy backfires as one of Chink's accomplices stabs him. While recovering in the infirmary, Leone learns from another inmate that Chink has conspired to harm Melissa. Whipped into a frenzy, Leone is met with betrayal by Dallas, who leads him into a trap at the warden's behest.
Trapped and exposed, Dallas faces dreadful consequences for his betrayal. The warden cruelly schemes against both men, leaving them vulnerable to the malicious guard staff. In a harrowing encounter, Leone engages in fierce battles against sadistic guards and endures unimaginable trials. In a dramatic display of his spirit, Leone prevails, enduring perilous confrontations that will test the limits of his courage.
With righteous fury boiling over, he forces Drumgoole into the very execution chamber intended for misdeeds. He secures the warden to the electric chair and threatens to execute him. As guards surround them with weapons raised, Leone reveals Drumgoole's wicked plot to prolong his sentence. But when he acts, nothing happens, having intended the whole affair to expose the warden's true colors. This prompts a judicial inquiry into Drumgoole's malevolence.
Ultimately, the result sees Leone released after serving only the original time required. With the cheers of his fellow inmates echoing in his ears, Frank walks out of Gateway one last time. He shares parting words with Eclipse and receives a cigar rumored to have been gifted by Fidel Castro. As he steps into a new dawn of freedom, he warmly embraces Melissa, leaving behind the prison's grim shadows forever.
