Some of Australia's most intriguing investigations are put under the microscope with viewers having the chance to play detective. Tonight, a young couple mysteriously disappear after a romantic picnic in La Trobe Valley and gruesome discovery in Sydney's Blue Mountains has detective baffled.

Is a man driven to kill the woman he loves? Or is she another fatality in an underworld hit? Also an innocent mum answers a mysterious knock on the door and is struck in the head in a barbaric attack. Is her husband to blame? And an elderly man is brutally bashed to death in his home. With no clues in sight could a pacemaker prove to be the key in catching his killer.