Devlin and Brooks investigate the death of a four month old baby, Alex. It's initially believed to be a cot death or SIDS. The pathologist finds serious injuries however that are consistent shaken baby syndrome. Four people had regular access to the child including the parents, Suzanne and Michael Rains, their nanny Layla Merton and Michael's ex-wife and business partner, Andrea. Their initial focus is on the nanny, who it turns out had been fired by a previous employer. The police also get evidence that her boyfriend Lloyd Benson had spent the evening with her, something she didn't disclose in her interview. The Crown pursues charges against both Layla and Lloyd but James Steel is afraid doubt about which of the two actually shook baby Alex may lead a jury to find them both innocent. A lie gives them the information they need to find who is responsible.