A psychopath the police have dubbed "Billy Dead Mates" is targeting pairs of best friends, and killing them one by one. Before they die, each victim is given a small white book. For months, detectives have failed to catch Billy, or figure out what the white books symbolize and why the killer leaves them behind. A woman, scared by what she's seen on the news, comes forward. What she reveals shocks the investigators and adds another troubling layer to an already complex case.