The British FrontLine: (Codename Orcus Book 2) by Thomas J Eyre

Patrick Regan is a man on a mission.

Expertly trained by the Royal Marines and with crack sniper skills, he’s always taken the fight to the enemy. However, now he realizes that while he’s been away, Great Britain has come under attack.

His parents are dead, his sister is missing, and he’s getting zero help from the authorities…