One year after the events of the previous film, Bartleby Trey Loney Livingstone and his dog Budderball Jeremy Shinder spend the summer at the farm run by Bartleby’s grandfather, Marvin 'Gramps' Livingstone John Ratzenberger. On Bartleby’s twelfth birthday, Marvin hands him the first issue of a comic titled Kid Courageous and Captain Canine, which retells the origin of a superhero from the distant planet Inspiron. The story introduces Captain Canine Colin Hanks, a defender sent from Inspiron to Earth to safeguard a set of powerful Rings, a mission complicated by the warlord Drex John Michael Higgins who vies to claim those Rings for himself. The tale also brings in Queen Jorala Fiona Gubelmann, whose caution about the journey colors the adventure. In the climactic sequence of the comic, Drex attacks; Drex appears to be defeated, and Captain Megasis, the loyal carrier of the Rings, lands safely on Earth with the Rings in tow.
The very next day, Bartleby’s dogs unearth the Rings in a barn, and a new sense of purpose awakens in them. Bartleby becomes the storyteller, recounting how a grown-up Jack Schaeffer Jason Earles joined Captain Canine on Earth to fight crime, with Jack chronicling their deeds in comic form. As news of the heroes spreads, Captain Canine detects the Rings’ energy, and he and the now-adult Jack begin tracking their source alongside Drex, who has somehow survived. In a remarkable turn, the Rings grant the canine friends extraordinary powers: Rosebud gains incredible speed, Mudbud becomes invisible, Budderball possesses super strength, B-Dawg flexes with remarkable agility, and Buddha wields telekinesis. The five dogs— Budderball [Jeremy Shinder], Rosebud [Genevieve Hannelius], Mudbud [Ty Panitz], B-Dawg [Cooper Roth], and Buddha [Tenzing Norgay Trainor]—decide to use their gifts for good, with Captain Canine [Colin Hanks] guiding them as they begin to master their abilities.
Drex lands near Marvin’s farm, possessing a pig and pressing further into the search for the Rings. Sheriff Dan [Michael Teigen] is skeptical of what he sees and fails to believe the extraordinary events unfolding, which leads to a tense confrontation as Dan pursues his own investigation. Drex’s disruption escalates when he commandeers Marvin’s truck and crashes into city hall, triggering a swift chase that lands him in police custody for a time. As Bartleby, the other children, and the dogs follow the strange disturbances in Fernfield, Drex captures the kids by locking them in a barn, while he uses his ship’s weaponry to direct a meteor toward the town and ignite a violent lightning storm.
In the ensuing showdown, Captain Canine faces off against Drex and is killed in the clash. The Buddies draw on the lessons they learned, and with a rallying push from Marvin, who uses a lightning rod to deliver a cathartic jolt, they overwhelm the villain. Drex’s weaponized Rings turn out to be fake, and his ship loses control, crashing into the meteor and meeting a fatal end.
With the crisis averted, the Buddies use the Rings to resurrect Captain Canine, who returns to Inspiron alongside Monk-E [Atticus Shaffer] and Jorala [Fiona Gubelmann], while Jack and Bartleby celebrate by creating a new comic series about the heroic dogs.
