In 1687, the infamous pirate Captain Yellowbeard (portrayed by Cheech Marin) wreaks havoc on the unsuspecting ship El Nebuloso, helmed by a Spanish inquisitor. With his clever second-in-command, Moon (actor not specified), having devised a daring scheme, Yellowbeard makes off with a treasure trove from the Spanish Main. However, Moon's reckless actions lead to a grim fate as Yellowbeard punishes him by severing his hand for breaching the revered code of pirate honor.
Twenty years later, Yellowbeard finds himself behind bars in England, where he has cleverly concealed the secret location of his buried treasure from his captors and the crafty spy, Gilbert (actor not specified). Commander Clement, a formidable Royal Navy officer and head of Her Majesty's Secret Service, taunts Yellowbeard by unnecessarily prolonging his imprisonment, fueling the pirate's ire as he bides his time for freedom.
As Yellowbeard prepares to escape, he seeks out his wife Betty (actress not specified) at her tavern, hoping to reclaim the treasure map etched onto their son Dan's (played by Martin Hewitt) scalp. Unbeknownst to him, Betty has tattooed the map on Dan's head, making it a target for those eager to find the loot.
Meanwhile, both Commander Clement and Gilbert receive intel about Yellowbeard's whereabouts, igniting a thrilling game of cat and mouse as they attempt to capture him. Blind Pew, a mysterious informant, tips off Clement but soon finds himself exposed by Gilbert as a government agent. The patrons of the tavern turn against Pew, yet he remarkably navigates the chaos.
As Yellowbeard resumes his quest for riches, he encounters Dan, now a grown man willing to assist his father in locating the treasure. However, Yellowbeard deems Dan unfit for piracy due to his gentlemanly upbringing under Lord Lambourne (actor not specified). In a moment of desperation, Yellowbeard foolishly attempts to sever Dan's head, but Clement's men intervene just in time.
Together, Dan and Lambourne seek refuge with Dr. Gilpin (actor not specified), a botanist hiding Yellowbeard. They concoct a plan to disguise the pirate as a botany aficionado, embarking on a trip to Jamaica disguised as an expedition. Betty agrees to help them for a cut of the spoils, though her transparent deceit only heightens Commander Clement's suspicions.
While Dan's crew books passage in Portsmouth, they find themselves ensnared in Moon's devious ploys. Moon cunningly enlists Dan, Lambourne, and Gilpin onto the Lady Edith, commanded by Captain Hughes (actor not specified). The crew endures harsh discipline at sea, culminating in a confrontation between Dan and his cruel tormentor, Mr. Crisp (actor not specified), who knocks him unconscious.
Secretly stowed away on the ship, Yellowbeard springs into action just in time to reclaim the map from Crisp and sends him into the water. Moon then reveals to Captain Hughes that Dan is Yellowbeard's son, leading to the arrest of Dan, Lambourne, and Gilpin on charges of mutiny. However, Moon orchestrates a mutiny, installing Dan as captain of the Lady Edith. Under the cover of night, Yellowbeard stealthily alters the ship's course, casting suspicion on both Dan and Moon.
The plot thickens as Clement's frigate unexpectedly converges with the Lady Edith. Seizing the chance to mask his intentions, Clement hoists the French flag, leading the Lady Edith into a feigned battle only to retreat strategically while maintaining the guise of secrecy.
Eventually, Yellowbeard, Dan, and their companions arrive at an island matching their cryptic map. However, their peaceful exploration soon escalates when they discover that El Nebuloso has built a fortress there, resulting in Dan's capture by the pirate's henchmen. With Lambourne and Gilpin attempting a rescue, they find themselves pitted against Nebuloso's brutal forces, who are swiftly dispatched by Gilpin's unique botanical concoction.
As tensions rise, Nebuloso holds Dan hostage, trying to extract treasure location details. Yet, Yellowbeard emerges, and Nebuloso's fear becomes palpable. In the ensuing chaos, Nebuloso unwittingly stumbles into an acid pool, meeting a grisly end.
The arrival of Moon and his men ignites a fierce sword fight, which Yellowbeard abandons in pursuit of the treasure. Meanwhile, Dan must fend off Moon's relentless attacks, ultimately receiving unexpected help from Triola, Nebuloso's daughter, who has fallen for him. With a decisive kick, Triola sends Moon into the acid, granting Dan some much-needed time.
The situation intensifies as Clement and his soldiers reach the island, guided by Betty's navigation skills. As all elements collide, Dan reunites with Yellowbeard, who, in a moment of desperation, cuts off Dan's hair to confirm their map's accuracy. Ultimately, this impulsive act leads them to the treasure, where Yellowbeard reveals another shocking truth: he is indeed Dan's long-lost father.
As Clement and his men claim the treasure in the name of the crown, Triola finds herself drawn to Clement, her affections momentarily shifting. This sets the stage for a climactic showdown involving Dan, Yellowbeard, Lambourne, Gilpin, Betty, and the unpredictable Moon. Ultimately, it is Dan who triumphs, claiming the treasure for himself and unfurling the Jolly Roger alongside his new allies: Lambourne, Gilpin, Betty, and the haunting legacy of Yellowbeard.
