Stay Alive by Simon Kernick

One witness: you’re on a trip with your family, miles from anywhere. A shot rings out - and your whole life changes in an instant.
One secret: a woman is racing towards you, chased by three gunmen. Although you don’t know it, she harbours a deadly secret. She’s in terrible danger. And now you are too.
No escape: you’re running, terrified, desperate to find safety. You know that the men hunting you have killed before. 
And if they catch you, you’ll be next…