"Chocolate Underground" is a 12-episode anime series based on the novel "Bootleg" by Alex Shearer. Set in a dystopian future, the story unfolds in a society where the Good for You Party has risen to power and imposed strict regulations on unhealthy foods, including chocolate. The government enforces these laws through the Health and Happiness Brigade, which conducts raids to confiscate and destroy contraband sweets. The narrative centers on two teenage boys, Smudger and Huntley, who rebel against this oppressive regime by creating an underground network to distribute illegal chocolate.

Smudger, the more impulsive and daring of the two, devises a plan to smuggle chocolate after discovering a hidden stash in an abandoned factory. Huntley, his cautious and thoughtful friend, reluctantly joins the operation, driven by a desire to resist the government's overreach. Together, they establish a secret chocolate shop called "Chocolate Underground," catering to a growing community of chocolate enthusiasts who risk punishment to satisfy their cravings. The boys' efforts attract the attention of the authorities, particularly the zealous Inspector Archibald Cripps, who is determined to eradicate all traces of chocolate from society.

As the story progresses, Smudger and Huntley face increasing challenges, including betrayal, close encounters with the Brigade, and the moral dilemmas of their actions. Their underground movement gains momentum, inspiring others to challenge the government's control. The series explores themes of rebellion, freedom, and the consequences of authoritarianism, using the prohibition of chocolate as a metaphor for broader societal restrictions. The characters' struggles highlight the tension between individual desires and collective control, culminating in a climactic confrontation that tests their resolve and the future of their movement.