The film is set during the timespan of The Fellowship of the Ring. It takes place 17 years after Bilbo Baggins's 111th birthday party and just prior to Frodo Baggins leaving the Shire for Rivendell. The wizard Gandalf fears that Gollum may reveal information about the One Ring to the Dark Lord Sauron, and sends the Ranger Aragorn, heir of Isildur, on a quest to find him.
The story opens with a brief prologue about the ring's disappearance before cutting to Aragorn and Gandalf (Patrick O'Connor) at an inn in Bree. Gandalf explains his concerns about Gollum's knowledge of the Ring falling into enemy hands, and asks Aragorn to find the creature with his tracking skills. After initially having little luck, Aragorn crosses paths with a fellow ranger and distant kinsman named Arithir , a Ranger of the North, who claims to have heard rumours about a creature that has been stealing fish from local villagers; there follows a brief glimpse of Gollum's hand reaching into a woman's kitchen window to steal a fish.
Aragorn and Arithir part ways, and Aragorn encounters and kills a pair of Orc scouts in the forest. He soon locates Gollum by a fish pond afterwards and captures the creature in a snare trap. Having secured the whining and protesting Gollum inside a sack, Aragorn sets out for Mirkwood. He briefly spots a Nazgûl in the woods, but avoids it. Later that same day, he is attacked by an Orc squad but defeats them. He collapses beside a patch of Athelas flowers and has a vision of Arwen in Rivendell.
Aragorn regains consciousness at dusk and discovers that Gollum has escaped from the sack. His search for the creature lasts well into the night, but Aragorn eventually finds him hiding up in a tree. Gollum fearfully explains that a Nazgûl is coming — seconds later, a Ringwraith attacks Aragorn. After a short duel, the Nazgûl flees from a bright light created by the Elves of Mirkwood, who recapture Gollum and guide Aragorn back to their fortress.
The scene cuts to Gandalf emerging from Mirkwood's dungeons after interrogating Gollum. The wizard tells Aragorn that Gollum knows of Bilbo Baggins and The Shire, and explains that he must now go there to warn Frodo. Aragorn suggests sending the Hobbit to meet him in Bree, and Gandalf readily agrees. The film ends with Gollum speaking to himself in the dungeon, where he vows to kill "Bagginses" and reclaim his "Precious".