Mr. Hyde, alias Willie The Weasel, abetted by Hyde Dog, demands to be mayor of Big City, threatening its citizens with a sinister formula that turns them into evil Hyde-like creatures. Blue Falcon and Dog Wonder, assisted by the Scooby-Doo detectives, plan to trap the wily Mr. Hyde and agree to his request. Once this results, Mr. Hyde, via his terrible greed, is snared into a wild falcon fracus: Dynomutt captures Hyde Dog and the antidote that will save Big City, with Blue Falcon's Falconclaw scooping up the fleeing Willie The Weasel, b.k.a. Mr. Hyde. After being commended by the Mayor, Dynomutt, executing a heroic exit from City Hall, accidentally gets caught in one of Shaggy's Scooby-traps!

Dog Wonder and B.F., teamed with the Scooby-Doo crimestoppers, meet Lowbrow, a villain desiring to be king of crime employing the knowledge from the books of Big City University to further his dastardly schemes. This primitive thief unwittingly leads Blue Falcon, Dynomutt and Scooby Doo and company to his lair, where they discover his latest plan: robbery of Big City Mint! Blue Falcon and Dynomutt set a trap for Lowbrow and thwart his evil plans, using an ""Instant Delayed Action Falcon Balloon,"" which captures him and neatly deposits him into prison. Later, at a restaurant, Blue Falcon and Dynomutt treat Scooby and friends to a turkey dinner, for their help in apprehending Lowbrow. Dyno volunteers to carve the turkey, but, instead of a Dyno-carving Knife, his paws malfunctioningly turn into Dyno-Mallets, which pound the poor turkey mercilessly flat. (""Anybody for turkey pancake?"")

The Daring Duo encounter the sinister Swamp Rat and Mudmouth, who've been hijacking trucks in the Bogmyer Swamp for the purpose of stealing their pumps. They use them to pump half of their swamp into Big City, turning it into Bog City, a giant swamp so muddy the citizens desert the city, leaving it unprotected and easy fair game for The Swamp Rat and Mudmouth. Blue Falcon and Dog Wonder, teamed with the Scooby Doo crimebusters, manage to extricate themselves from becoming gator bait and rush to the aid of the oozy Big City to lure the swampy thieves into the open. There, B.F., to allay Swamp Rat's suspicions, disguises Shaggy Rogers and Scooby-Doo as Blue Falcon and Dynomutt, respectively, and have them going the other way with the real Daring Duo posing as expensive gold statues at The Big City Convention Hall. The wily thieves, thinking B.F. and D.W. are heading elsewhere, feel free to steal the gold statues. When they learn of Blue Falcon's ruse, they flee into the swamp, only to be