Roy and Bella investigate a murder on a council estate after a teenager is stabbed to death , with signs initially pointing to it being drug-related, but the victim's parents are adamant that their son had nothing to do with drugs. The investigation brings Grace face to face with someone from his past and stirs up old demons that worry Bella, with the case placing one of the team in grave danger. Meanwhile, Branson's investigation into a masked armed robbery leads to tensions in CID