Enemy Action (Book 3 of The Imperial Marines Saga) - Terry Mixon - Bog

Know your enemy like you know yourself. Andrea Tolliver and her friends are now Imperial Marines, sworn to protect the Terran Empire from all enemies. Too bad she hasn't even had time to make friends in her new unit before civil unrest sees them deployed. Once is happenstance. Twice is coincidence. Separated from their unit, they must discover who is really behind the unrest and stop them by any means necessary. When the enemy strikes from the shadows, they must stand and fight. If they fail, the Empire will never be the same. Three times is enemy action.