Superman, who grows up with a
Kryptonian Labrador Retriever named
Krypto, goes by the name Clark Kent in everyday life. Krypto feels jealous when Superman starts dating
Lois Lane, so Superman goes to an
animal shelter to find Krypto a friend. A
Boxer named
Ace tries to escape the shelter, but Krypto stops him. Later, Superman and Krypto spot their archenemy,
LexCorp CEO
Lex Luthor, reeling in a meteor strapped with orange
kryptonite with a tractor beam, intending to gain superpowers. He is easily defeated as the two are aided by the
Justice League, formed by Superman himself,
Batman,
Wonder Woman,
The Flash,
Green Lantern,
Cyborg, and
Aquaman. Meanwhile, Lulu, a
guinea pig test subject from LexCorp sent to the shelter who is blindly loyal to Luthor, reels in a piece of orange kryptonite with her own tractor beam, which gives her
telekinesis and allows her to escape the shelter, setting it ablaze while doing so. Unbeknownst to her, everyone else in the shelter also gains superpowers: Ace is now super-strong and nigh-invulnerable; PB, a
potbellied pig, can change size; Merton, a nearsighted
turtle, becomes super-fast; and Chip, a paranoid
squirrel, gains
electrokinesis. Using their new powers, they escape the burning shelter. While at home, Superman and Krypto have an argument when the former plans to propose marriage to Lois. However, Clark is captured by Lulu when she weakens him with kryptonite. Krypto tries to save him, but loses his powers after unknowingly eating a tiny shard of a green kryptonite hidden inside a piece of
Jarlsberg cheese. Later, Krypto comes across the shelter pets, who agree to help him. Meanwhile, Lulu gives powers to and recruits a group of guinea pigs, captures the Justice League, and heads to Stryker's Island to free Luthor. The shelter pets try to stop her, but fail miserably; in the process, Lulu taunts Krypto about Clark's engagement plans and even shows him the engagement ring. They regroup in the
Hall of Justice, where Ace reveals to a distraught Krypto that he used to have owners as a puppy: a family with a toddler. One day, when the wandering toddler was about to fall down a flight of steps, Ace accidentally bit her arm to pull her to safety. Upon seeing the bite-marks, the parents assumed Ace attacked her and sent him to the shelter, though Ace stands by his actions and ideals. Encouraged, Krypto leads the pets to LexCorp. While there, a
kitten named Whiskers, (who Lulu rescued from the shelter after she set it ablaze the night she and the others gained their powers) who can now create weapons at will, attacks them, but the team traps her. At Stryker's Island, the shelter pets confront Lulu, but put themselves in prison cells when she threatens to kill Krypto. Lulu frees Luthor, who then betrays her and locks her in his cell while freeing
Mercy Graves. Lulu breaks out easily and decides to destroy the Justice League and Luthor herself. The Kryptonite shard passes through Krypto's system, restoring his powers. He breaks himself and the other super pets out of prison, and attempts to free the Justice League, but Lulu launches them into space along with Luthor, betraying her remaining henchmen while doing so. In order to stall Krypto, she attempts to kill Lois. However, the other super pets rescue the Justice League while Krypto saves Lois and defeats Lulu, but she absorbs the orange kryptonite, becoming a mutated
kaiju-sized version of herself. The League and the pets team up to stop her, but she gains the upper-hand. Realizing Lulu has become too powerful, Krypto decides to use the "Solar Paw Punch", a move that can defeat any supervillain, but will kill the user. The attack causes a massive explosion that knocks the kryptonite out of Lulu's system, causing her to lose her powers and return to normal size while Krypto accepts his fate. Ace uses his invulnerability to save him. Shortly after, Lulu's redeemed henchmen, Mark and Keith, trap her in a hot dog stand for her crimes and betrayal. In the aftermath, Krypto allows Clark to marry Lois. The shelter pets, Mark, and Keith get adopted by the rest of the Justice League: Ace by Batman, PB by Wonder Woman, Merton by The Flash, Chip by Green Lantern, Mark by Cyborg and Keith by Aquaman. Sometime later, the pets have formed their own superhero team called the "
League of Super-Pets". In a
mid-credits scene, Luthor is still trapped in his prison asking any passing super-animals to free him, without success. Meanwhile, Lulu is freed by Mercy, who adopts her. In a
post-credits scene, Krypto and Superman encounter
Black Adam and his dog, Anubis, but Krypto tricks them into flying to
Pluto. ==Voice cast==