Humanity has stretched out across the stars and formed a new Frontier. Normally, the brave men and women of the Wall Guard stay on Earth to protect humanity's home, but when her lieutenant is abducted by alien raiders, Addi abandons her post and ventures into the Frontier. She enlists the help of her trainee and a young cartographer, but every expedition needs a guide and there is none better than the disavowed Frontiersman, Jackson August.

While they search for the missing lieutenant, Addi and her crew unknowingly interfere with the plans of the mysterious Cassian Fawkes.

Can Jackson get over his dark past? What secrets does he hold in regard to Addi? Who Is Cassian Fawkes and what is he planning against humanity's home?