A real-life industrial accident that occurred around 12:37 pm on July 10, 1976, in a small chemical manufacturing plant owned by ICMESA where there was a release of 6 tonnes of chemicals from pressure tank, including 1 kg of dioxin. The tank's release sent the chemicals in nearly 7 sq miles. Within days a total of 3,300 animals, mostly poultry and rabbits, were found dead.
Thousands of inhabitants in the town were exposed, many suffering from skin lesions and chloracne. The plant's company did not notify the public nor the government for over a week that deadly dioxin had been leaked, and it took another week until evacuation occurred. 2 weeks worth of poisoning caused long-term health issues for residents. At the time abortion was illegal in Italy but the government temporary authorized it for the women in fear of severe birth defects.
The issues continued to compound when a governing body contracted a company to dispose of the waste barrels. The contractors illegally dumped the waste in northern France and had a notary falsify documents saying that the waste was properly disposed of. This was only discovered thanks to a Swiss intervention.
The disaster helped improve industrial safety regulations which were passed in 1982 called the Seveso Directive to prevent future accidents across Europe.
The anime follows a group of friends Giulia, Maria, Enrico, Lucio and Angelon during the disaster as they team up with a Japanese journalist Shiro Ando, and begin their own investigation of what's occurring (during the week long period of exposure when the ICMESA refused to notify citizens of the poison). As many animals are dying and people are getting sick. The children and Shiro discover deadly dioxin was released and inform Enrico's father, the town mayor, who evacuates all the citizens. Shiro continues investigating more and learns of the negligence of La Roche, a company who controls ICMESA. La Roche knew they were in violating of existing safety laws/protocols and destroyed evidence of their crimes. The children attend a press conference to ruin La Roche's reputation as the destroyed proof might not be enough in a court of law to punish them.
Giulia's pregnant sister, who opted to not abort, gave birth to a healthy girl. The happiness is short lived, as the baby prematurely dies from dioxin poisoning.