Little Liar by Leigh Rivers

Malachi Vize has always had one desire in life.
One goal. One deep obsession he could never give up on.
His foster sister Olivia.
For the first time, she’s chosen him over the entire world, and he intends to keep her in his firm grasp forever – but his happiness is soon shattered by powerful enemies who want to claim Olivia for themselves.
He had her.
But then he lost her.
Wounded and still wrestling with his own demons, Malachi is forced into unexpected alliances to hunt them down, but he won’t stop fighting until he gets her back.
No matter what it takes.