Alex Marshall: A Blade of Black Steel [2017] paperback

After five hundred years, the Sunken Kingdom has returned, and brought with it a monstrous secret that threatens to destroy every country on the Star. As an inhuman army gathers on its shores, poised to invade the Immaculate Isles, the members of the Cobalt Company face an ugly choice: abandon their dreams of glory and vengeance to combat a menace from another realm, or pursue their ambitions and hope the Star is still there when the smoke clears. Five villains. One legendary general. A battle for survival.