Codename: Nightfall, a woman of discreetness and deception who loves to stay in the shadows like a sly fox, was bestowed the power to lead the group of assassins called the Night Hounds. ​In pursuit of the perpetrators who attacked the phantom island of the Hounds nine years ago, Nightfall meets a remarkable agent known as Apollo of the White Government, who has the same goal as her: to take down the Suns. ​Can the two be able to cooperate with each other, having totally opposite senses of justice and morals? ​Or can love bind them together?