A trip to the store for Custard, Buzz, Brianna, Jazz and Kea is interrupted by the arrival of super-villain Dr Gloom and his plans to gloomify the town using technology that has weaponized depression.

Cornered in Dr Gloom's secret underground lair, Custard must rescue Kea and escape with the super-villain's most vital piece of technology: 'The Thingy'.

Recovering from their recent tussle with Dr Gloom, the kids devise a scheme to plant a secret spy camera inside his super-villain lair in order to monitor his nefarious activities.

During a particularly hot day, Dr Gloom and his assistants Colin and Agar turn their gloomifying 'Depresso' gas into ice-creams and attempt to distribute them to the unsuspecting residents of the town.

Impressed by the sold-out crowds attending the performance of visiting stage magician Cheerio The Great, Dr Gloom hatches a scheme to replace Cheerio with himself and gloomify the audience.

When a televised talent show comes to the small town of Doodle, Dr Gloom infiltrates it with another cunning Depresso weapon, unaware that Jazz is performing at the show and that Custard, Brianna and Buzz are nearby to foil his plans.

Plagued by mounting bills, Dr Gloom plans to steal The Uno Pizza - a fossilized artifact reputed to be the world's first pizza - from the Doodle Art Gallery and sell it off profit.

After ruining preparations for Jazz's birthday party, Buzz goes to Mr Fadtastic for help on picking out a birthday present and accidentally overhears Dr Gloom's next nefarious plan.

Dr Gloom and Agar infiltrates the Doodle High School Science Fair to unleash their Depresso Gas on the unsuspecting patrons.

Agar reveals that she has been secretly working on a top-secret weapon: The Gloomsday Machine, a device powerful enough to gloomify the entire town of Doodle with one fell swoop. The only problem is that it needs a power source.

When a mysterious alien artifact is ejected from a UFO crash-site, Dr Gloom mounts a plan to attack Custard's treehouse and steal the device to use as a power source for The Gloomsday Machine.

With Kea injured, Custard having lost his confidence and The Gloomsday Machine fully activated, Dr Gloom is now poised to unleash his master-plan to gloomify the entire town of Doodle.