'Hidden Killers' sees Jane Tennison acting as a 'decoy' prostitute, with the hope of capturing a suspect wanted for numerous sexual assaults. The attacker is drawn in and put under arrest. Commended for bravery in the case, Jane is given CID status and moves from Hackney to Bow Street Station as Detective. Her first call-out is to a non-suspicious death. The victim is a young mother, drowned tragically in her bath, leaving a bereft and doting husband...