Ronnie and Matt tackle a particularly upsetting case involving the death of a baby. When six-month-old Alex Raines is reported dead, what initially seems to bear the hallmarks of a tragic cot death is later diagnosed as shaken baby syndrome. The murder investigation that follows throws up many possible suspects, including an apparently neglectful mum, an absent dad, a resentful nanny and her irritable boyfriend.
The detectives have their work cut out to get to the bottom of what happened, and matters are just as complicated for the Crown Prosecutors when,during the trial, new evidence casts doubt on their case. Pitted against the formidable Helena Marsden (Jemma Redgrave), James and Alesha have some investigating of their own to do. In the process, every aspect of the family in question is pulled apart.