The Replacement - Season 1 Episode 2

Ellen tries to juggle her new baby with her return to work and her investigation into Paula. She finds evidence that her boss was having an affair but her only lead is Paula's ten-year-old child and a former colleague of Paula's, neither of whom want to speak to her. Paula discovers Ellen's investigation and engineers a humiliation from the client and a warning visit from social services. Ellen eventually confronts Paula and forces her to confess what she's been hiding.