Tension on the tube network threatens to boil over, and security is stepped up. The accidental verdict in the first death is called into question and the witnesses are brought in for interview. Amongst them is Lana Sutherland, a young hotel worker who has taken in a homeless man, Owen. DI Nelson lets Lana slip through the net before he realises she may be harbouring a dangerous killer.

Nikki helps Nelson unearth the mystery of his father's death, allowing him to confront and resolve the childhood memories that haunt him. He refocuses on the case and, with Jack and Nikki, discovers the missing key that links the victims.

Daniel Garvey is found dead in his car. Social worker Louise fears that he may have been killed by his 16-year-old stepson Kevin, who has just come out of care.

Nikki, Jack and Thomas focus in on Lizzie Craddock's movements on the night of Barge's murder. Jack and DI Gina Conroy discover Lizzie's last known location but fear what they may find there.

Louise comes under further pressure when she is forced to make a call on whether a sick child, Ricky Mansfield, is being abused by his parents.