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. The police are on edge; the public in a panic. Then 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.