It was a normal time on earth,as people went about their daily life activities and no one gave a damn about the other.
Then in the course of space exploration NASA decided to take a bold step by landing on Mars,Astronauts started exploring the planet and taking samples to be send back to earth for scientific purposes.
After a week on Mars they decided to return to earth with their bounty where scientific research were conducted on the finds on Mars.
Many experiments were conducted on the Martian finds and including those finds was a gas collector which after much experiments was declared the gas dangerous.
Then an incident occurred as a vehicle transporting one of NASA's technological advancements was hijacked and among those advancements was the gas,the hijacker's after taking a hold of the tech decided to dispose of the gas since it was useless to them and so they decided to destroy the collector containing the gas.In doing so they were exposed to the gas which made them go berserk and started attacking people nearby and biting them in a sort of zombified fashion and all the bitten victims also started behaving like them