Deathfire by Nick Kyme

Vulkan lies in state beneath the Fortress of Hera, and yet many of his sons still refuse to believe that he is truly dead. After a seemingly miraculous rescue by the Ultramarines, Artellus Numeon, once captain of the Pyre Guard, urges the other Salamanders on Macragge to leave Imperium Secundus and return their primarch's body to the home world of Nocturne – there to be reborn in the flames of Mount Deathfire. But Numeon grapples endlessly with his doubts and fears for the future of the Legion, while their foes seek to carve out new destinies of their own...