When teenager Caitlin Harris is knocked down in a hit and run, Sergeant Stone and Pc Tony Stamp trace the car to a man called Ryan Davidson. Ryan tries to protect himself by claiming that the car was stolen, but Stamp isn't convinced. He orders a breathalyser test, which Ryan fails. At the hospital, Pcs Sally Armstrong and Ben Gayle discover that Caitlin's companion at the time of the accident, Kim Yates, isn't actually her mum, as assumed. But Sally and Ben soon discover that Kim is lying - she really is Caitlin's mum, but was forced to give her up for adoption at birth and had revealed the truth to her shortly before the accident. Later, Ben and Sally receive a call to say that Kim has parked her car on the edge of a wharf. Alarmed, they race to the scene. As Kim drives into the river, Inspector Gina Gold tells Sally she will lose her job if she attempts to save her. Sally throws her warrant card at Gina's feet and jumps in anyway...
