In DARK: Underground, the third book of The DARK Series, Nathan has been fully trained and is assigned to a DARK team. Before he starts his first mission, Nathan is granted time off for Christmas. While visiting his brother, a horrific murder takes place and the wrong person is blamed. Nathan hurries to make things right before he is due back at the base. Once the chaos is behind him, Nathan and his new team head to The Underground. Their mission is to find a mysterious doctor that may be close to creating a cure or vaccine to the Canny virus, known as CANVID-17. Nathan fights through the dark underground in hopes for a better future.