Greenway Modern International School in Shahdara, Delhi. The school is relatively isolated, but large enough for the outbreak to spread rapidly. It's a typical day until the chemistry class goes wrong.
In the chemistry lab, a group of 12th-grade students are conducting an experiment involving volatile chemicals. They unintentionally create a gas that, when inhaled, turns people into zombies. This gas spreads quickly throughout the school's buildings. The students who are working on the experiment are either unaware of the danger or are too focused on their work to notice at first.