Years before meeting Priscilla Asagiri, Leon McNichol had a violent run-in with a Boomer, a type of advanced android. He transferred to the AD Police, the department tasked with crimes concerning Boomers. Along with seasoned policewoman Gina Marceau, Leon tries to curb the violent crimes that have begun to plague MegaTokyo. However, these cases grow increasingly complicated, threatening to upend the social order with the debate of what it means to be a human.