The movie begins with an elderly Spartan examining an unattractive, talking infant, a nod to the ogre from Shrek the Third. This baby is ultimately abandoned due to its deformities. In contrast, a second baby, who is Vietnamese, is adopted by the famous couple Brad Pitt and Angelina Jolie. Enter Leonidas (played by Sean Maguire), who astounds all with his natural six-pack, biceps, and beard from day one. He is quickly embraced as a Spartan and undergoes rigorous training, which includes battling his grandmother and surviving extreme hardships reminiscent of Casino Royale.
After being exiled into the wilderness, Leonidas faces a brutal winter and a gangster penguin, a cheeky reference to Happy Feet. Upon returning from his trials, dressed in a penguin skin hat, Leonidas witnesses Margo (Carmen Electra) engaging in an erotic dance and promptly proposes to her, which leads to her cheeky response of revealing the combination to her chastity belt.
Years later, while training his son, Leonidas receives word from Captain (Kevin Sorbo) about a Persian messenger's arrival. Accompanied by the Spartan traitor Traitoro, the messenger is there to present Xerxes' demands for Sparta’s capitulation. Greeting the messenger with traditional Spartan customs, which include high-fives for the women and extravagant tongue kisses for the men, Leonidas quickly grows furious. His anger peaks when he catches the messenger disrespecting him by making out with his wife, prompting him to send the messenger into the dreaded 'pit of death'. Ignoring Traitoro's warnings about the messenger's guards, Leonidas kicks them in as well, alongside other pesky figures like Britney Spears and Sanjaya Malakar.
Determined to confront the Persians, Leonidas consults the Oracle, portrayed as Ugly Betty, who ominously tells him that death awaits him should he go to war. After a night spent contemplating with his wife, Leonidas gathers his troops only to discover that just 13 Spartans, rather than the famed 300, are willing to join him due to their particular criteria of being “Hunky with deep Mediterranean tans, hot bods, and well-endowed.” Among these brave souls are Captain, his son, Sonio, and a rather unfit Spartan named Dilio, humorously described by Captain as having "a lot of heart...and nice man boobs."
As they reach the Hot Gates, they encounter an oddly deformed Paris Hilton (also played by Parker), who reveals a secret goat path that Xerxes could exploit. When she petitions to become a Spartan, Leonidas denies her due to her inability to wield a spear effectively. The Spartans end up battling Xerxes’ messenger and his Immortals, triumphing in a victorious dance contest that ends with the villains falling off a cliff. Impressed by his tactics, Xerxes (Ken Davitian) personally approaches Leonidas with an offer to bribe him; Leonidas boldly chooses to bring him down instead.
The conflict evolves into a "Yo Momma" showdown, resulting in a Spartan victory despite Dilio facing an eye injury. However, just when success seemed guaranteed, Paris Hilton betrays them by informing Xerxes of the goat path in exchange for riches. This betrayal leads to a climactic battle where the Persians employ their secret weapon: a CGI version of Ghost Rider and Rocky Balboa, leading to Sonio's tragic demise. Leonidas vows to avenge his fallen soldier, leading them both into an intense face-off against Xerxes.
The showdown culminates in a humorous twist—in search of vengeance, Leonidas inadvertently plays Grand Theft Auto as he encounters Xerxes, who absurdly transforms into "Xerxestron" via a mysterious "Transformer Cube." But in a moment of comic fate, Xerxestron trips over his own extension cord, resulting in Leonidas’ prophecy of his fall becoming a reality, although Leonidas also meets his own tragic end in the process.
Later, the story shifts back to blindness-stricken Dilio, who returns to Sparta a year later to recount the legacy of Leonidas. Rallying a hundred true Spartans and legions of CGI warriors, Dilio surprisingly leads his forces the wrong way, landing them in Malibu where they accidentally bump into a stumbling Lindsay Lohan.
The film wraps up with an exuberant musical finale featuring I Will Survive by Gloria Gaynor, performed by all the characters in a lively segment reminiscent of American Idol.
