Casanova (AKA Terror), a Yorkshire terrier in P.U.P., must come out of retirement when the shed where his masters package and store homemade peanut butter is burglarized. That means Casanova’s son, Hunter, will receive on-the-job training. A scurry of squirrels and its allies (including a cop-hating fly, lizard and crow) promise to make “Terror’s” life hell as they attempt to lift the “gold,” as it’s known to squirrels. During Casanova’s last solo patrol, he captures a young, sassy squirrel, named Squirt O’Hara, bent on proving her brother, Pete, wrong and making it to the shed. Upon seeing his first presumed “kill” and what he determines to be such an innocent-looking creature, Hunter has a change of heart. Out of view, Hunter keeps Squirt close to him for the night. When she miraculously revives in the morning, Hunter must nurse her back to health and keep her status secret from his father. It will prove an impossible task.

Meanwhile, Squirt’s brothers, Gregory and Pete O’Hara, plot revenge against Terror. They meet with a gang of squirrels, led by Honeynut Harry, and make a deal. Casanova in exchange for all the “gold” Honeynut wants. The following day, Hunter feigns illness to stay with Squirt. Casanova does his rounds alone. The squirrels strike back. Casanova is carried back unconscious. Hunter must now balance an ailing father with a nose for a resurrected rodent and the well-being of his adopted squirrel.

When Gregory turns missing, Honeynut Harry and his gang force Pete to the shed to collect the gold. He runs into a healing and vengeful Casanova instead. After a near escape, he finds Gregory and a great surprise: his living sister, Squirt. They plan her escape. Only Squirt has found her new home and wants nothing with the old. When Hunter reveals that he won’t be able to keep her safe under his care, Squirt forces him to escort her home. Juleye, a fly with an eye for spying takes this information to Liza the lizard, who together with Mr. Nightfeather the crow, make a final pact with Harry Honeynut’s gang. They will kidnap Hunter and use him as a hostage for ransom-all the gold they can stand-if Casanova wants his son back safe.