The nefarious Chairman Drek, portrayed by Paul Giamatti, addresses his followers, the Blarg, as they prepare to annihilate an abandoned planet. In a moment of comical reprimand, he catches one of his minions texting and instructs his robotic henchman, Victor Von Ion, to handle the situation. Displaying his ruthless demeanor, Victor resolves the issue by consuming the goon's phone before the villains successfully destroy the planet.
Meanwhile, in another part of the galaxy, the young lombax named Ratchet is tinkering away in his garage, working on a spacecraft for a customer. In a comedic mishap, he accidentally activates the ship's magnetic pull, resulting in a whirlwind of metal items flying toward the vessel. Despite the chaos, Ratchet manages to launch the ship, inadvertently ejecting the customer from his seat mid-flight.
Ratchet idolizes the heroic Galactic Rangers, including Cora, Brax, Elaris, and their charismatic leader, Captain Quark, who are in search of new recruits after multiple planets face destruction. Although Ratchet dreams of joining their ranks, his mentor, Grimroth Razz, advises him to think smaller to avoid disappointment.
In a twist of fate, Drek breaks out the notorious mad scientist, Dr. Nefarious, from prison to help construct an army of robots aimed at eliminating the Galactic Rangers. Nefarious harbors a personal vendetta against Quark, the very ranger responsible for his imprisonment. Among the new robotic creations is a defect labeled as insufficient, which attempts to escape Drek's wrath by fleeing in an escape pod.
Eager to join the Galactic Rangers, Ratchet heads to their city, where he witnesses Quark's flashy entrance, calling potential recruits forward. However, when Ratchet is brought in for an interview, Quark coldly tells him he lacks the qualifications to join their ranks. Disheartened, Ratchet heads home, feeling validated in Grim's caution against dreaming too big.
Fate intervenes when Ratchet discovers the escape pod containing the small robot and rescues him just before it self-destructs. He decides to name his new companion Clank. Soon after, Drek unleashes his robotic army upon the city, igniting a battle between the Rangers and Drek's forces. As the Rangers engage in combat, Ratchet and Clank soar above in Ratchet's ship. Demonstrating ingenuity, Ratchet utilizes the ship's magnetic pull to redirect the robots into the Rangers' ship, causing an explosive conclusion to the confrontation and garnering admiration from the onlookers.
Despite Ratchet's newfound recognition, Quark's jealousy simmers beneath the surface, as he grapples with the loss of his own spotlight. When Ratchet and Clank are officially welcomed into the Rangers, they begin their training. Clank finds himself in an office that doubles as a closet while Ratchet wrestles with an array of weaponry, failing hilariously at every turn.
The Rangers soon discover Dr. Drek's plan, which involves the sinister Deplanetizer designed to obliterate abandoned planets for his personal gain. Quark, seduced by the allure of fame, agrees to betray the Rangers, complicating their mission. As they move forward, their weapons system is compromised due to Quark's treachery, adding further peril to a tense situation.
Meanwhile, Victor hunts down Clank for a final showdown, but Clank cleverly responds by unleashing a rain cloud from his weapon that causes Victor to rust. As Ratchet learns of Quark's betrayal, they arrive too late to prevent the destructive power unleashed upon the inhabited planet.
Returning home in despair, Ratchet receives a wise reminder from Grim: to be a true hero, one needs to focus on doing what is right, regardless of grandeur. Renewed with purpose, Ratchet gears up for the final confrontation against Drek and his looming threat.
In a twist of events, Dr. Nefarious ousts Drek from power by employing a gun that magically transforms him into a sheep, effectively taking charge of the operation himself. When including the Rangers in a desperate struggle against the Deplanetizer, a last-minute plot from Elaris directs the blast away from innocent planets.
As Quark returns to righteousness, a climactic battle ensues between him and Nefarious. With the help of Ratchet, Nefarious is rendered defeated, and the Deplanetizer meets its end through a fiery crash.
As the victorious Rangers return as heroes, Quark embarks on an apology tour through the galaxy, while Ratchet and Clank solidify their bond of friendship as official Galactic Rangers. In a final scene before the credits, repair bots discover Nefarious's remnants at the crash site, teasing the imminent return of evil.
