"Chocolate Underground" is a manga adaptation of Alex Shearer's novel "Bootleg," set in a dystopian society where chocolate and other sweets have been outlawed by the government. The story centers on two teenage boys, Smudger and Huntly, who live under the oppressive rule of the Good for You Party. This authoritarian regime enforces strict dietary laws, banning all unhealthy foods, including chocolate, under the guise of promoting public health. The government's control extends to surveillance, propaganda, and harsh punishments for those who defy the ban.

Smudger and Huntly, disillusioned by the regime's overreach, decide to resist by creating an underground network to distribute illegal chocolate. They establish a secret club called the "Chocolate Underground," where members can secretly enjoy forbidden sweets. The boys' rebellion grows as they recruit more members, including their classmate Madeleine, who becomes a key ally. Together, they navigate the dangers of evading government agents, known as the "Chocohunters," while spreading their message of resistance.

The narrative explores themes of freedom, rebellion, and the consequences of authoritarianism. Smudger, the more impulsive and daring of the two, often takes risks to challenge the system, while Huntly, more cautious and analytical, provides strategic planning. Madeleine adds depth to the group with her resourcefulness and determination. As the Chocolate Underground gains momentum, the stakes escalate, leading to confrontations with the authorities and moral dilemmas about the cost of their rebellion.

The manga effectively captures the tension and urgency of the boys' struggle, blending moments of humor and camaraderie with the darker realities of living under an oppressive regime. The story builds toward a climactic showdown between the Chocolate Underground and the Good for You Party, raising questions about the power of collective action and the resilience of the human spirit in the face of tyranny.