Snap by Belinda Bauer

This is one of the first times that I can remember that a flat our murder mystery was long listed for the Booker Prize.  Wow!
The opening finds 11-year-old Jack Bright and his two younger sisters left in a car on a British motorway by their mother, Eileen, after a breakdown one summer day three years before the action in the present. Jack ventures out of the car in search of his mother only to find a phone booth with a receiver left dangling off the hook and his mother's body with a very distinctive knife nearby. Jack's father abandons the kids, leaving Jack to resort to a life of crime in order to avoid going into care.   In the present, pregnant Catherine While scares off a stranger who breaks into her West Country home; later, she finds a knife next to a birthday card her mother sent her. The message in the card had been crossed out and replaced with the words “I could have killed you.” The plot lines predictably overlap, and come to a united conclusion.