Claire Takes On The Galaxy by M S Lawson

Fleeing the wedding day from hell and her mother, Claire Williams enlists in the Stellar Marines Corps – recruitment slogan ‘Take on the Galaxy, Join the Stellar Marines’ – and is sent to defend the remote colony of Devil’s Pit. There she meets exiled bank robber, James, and his adopted daughter, and finds she must fight mysterious creatures called Shades in caverns as well as the enemy they call Mercs, who want the colony for the precious lift crystals mined there. In the meantime, James finds himself drawn into his own deadly, shadow battle to find a Merc agent among the colony’s marine officers.