It has been three years since the zombie virus broke out globally. Cities are now in shatters, streets filled with only the cries of zombies and smell of rotten meat. To evade zombie attacks, survivors built a number of safe quarantine areas on high ground or underground. One of the low ground quarantine areas is located at the center of Hong Kong Island, with tall walls on four sides. Hong Kong Island used to be an international center surrounded by the sea. After the outbreak of global zombie virus, all land-connecting bridges were cut off, and high-rise walls were built to protect the core areas. It was the least affected area. The World Health Organization set up one of its research centers here, gathering doctors and experts around the world to develop vaccines and carry out scientific research. The research center is called LAB 51 District, but to the average person, this is known as ZOMBIE LAB.