In 2096, on a remote planet, the Leprechaun, Warwick Davis, courts an alien princess named Zarina, Rebekah Carlton, in a nefarious bid to become king of her home world. The two strike an arrangement to marry, but each party secretly plots to kill the other after the wedding night to enjoy the marriage benefits: a noble title for the Leprechaun and the princess’s gold and jewels for Zarina, all while keeping their political and personal ambitions intact.
A platoon of space marines arrives to deal with mining interference and ends up killing the Leprechaun for stepping on their operations. Kowalski, Geoff Meed Kowalski, tries to steal the Leprechaun’s gold but is cut down by the Leprechaun’s lightsaber. A grenade then explodes, delivering a fatal blow to the Leprechaun himself. In a crude moment of bravado, Kowalski urinates on the Leprechaun’s body, a taunt that takes a dark turn as the Leprechaun’s spirit travels up his urine stream and into Kowalski, where the malevolent presence begins to manifest in disturbing ways.
The marines return to their ship with the injured Zarina, intending to return her to her home world and establish diplomatic ties. Onboard, the ship’s commander, Dr. Mittenhand, Guy Siner, outlines a chilling plan to use Zarina’s regenerative DNA to recreate his own damaged body. Elsewhere, the Leprechaun erupts from Kowalski’s body during a sexual confrontation, a grotesque reminder that the war between magic and metal has only just begun. The marines hunt the Leprechaun, but he proves elusive, outsmarting them and killing most of the crew with a series of gruesome and absurd traps.
While pursuing Zarina, the Leprechaun injects Mittenhand with Zarina’s DNA mixed with the remains of a crushed scorpion and tarantula, and then triggers the ship’s self-destruct sequence. A surviving marine, Sticks, Miguel A. Núñez Jr., rushes to the bridge to defuse the timer but is halted by a password prompt that blocks the safeguard. Mittenhand—now grotesquely transformed into a spider-like figure calling himself Mittenspider—ensnares Sticks in a giant web, a nightmarish trap that blends science with sorcery.
Meanwhile, the other survivors confront the Leprechaun in the cargo bay, and in their clash, he is driven to giant size after being hit by Mittenhand’s growth ray. The ship’s biological officer, Tina Reeves, Jessica Collins escapes to the bridge and frees Sticks by spraying Mittenhand with liquid nitrogen and shooting him. The remaining Marine, Books, Brent Jasmer, opens the airlock, hurling the gigantic Leprechaun into the cold void where he is swiftly sucked away and explodes.
Books rejoins the others at the helm, and they piece together the ship’s password, which turns out to be "Wizard"—a clue tied to Mittenhand’s earlier boast that he was like the Wizard of Oz. With the self-destruct halted, Books and Reeves share a quiet, awkward kiss, while Sticks gazes out the window and watches the Leprechaun’s enormous hand give him a final, mocking gesture as the danger finally begins to fade. The crew, battered and wary, must reckon with the bizarre blend of pharmaceuticals, magic, and military might that brought them to this strange, deadly frontier.
