The film opens with a recap of earlier events in the series as David Sloan writes a letter to his wife, Vicky.

After being framed for murder by Tong Po, David has spent the last two years in prison, while his wife has become the sexual captive of his old nemesis, who has since become one of the most powerful drug lords in Mexico.

On his way to the border, David enters a roadside bar and confronts a group of thugs harassing a young woman named Megan Laurence.

David arrives at the compound and is greeted by Darcy Cove, one of Po's many female sex slaves, who tells him that he must compete in the qualifying matches.

In an effort to gain more intelligence about David's wife, Lando enters a romance with Darcy and presses her for information while offering to help her escape from Po.

Meanwhile, David seeks to free his wife but is unable to find her since Po had her moved from her original cell as a result of his previous intrusion.

On the final day of the tournament, Po declares that all fights will be to the death and dismisses several fighters who are unwilling to risk their lives, but shoots them all dead as they depart.

Po announces that the tournament is a memorial to his late wife, Sian, who was killed five years prior when the DEA invaded his home.

After a brutal fight, David conquers his rival once again, but Bill takes Vicky at gunpoint, giving Po the opportunity to escape.

TV Guide rated it 2/5 stars and wrote: "Kickboxer 4 does proud by the franchise that gave the world Jean-Claude Van Damme".