Tonight's episode is called 'Immune' and was written by Nicholas Hicks Beach and is notable for starring no less than three Doctor Who alums (Adjoa Andoh who played Francine Jones, mother of Martha Jones (played by Freema Agyeman) plays a pathologist).
A bungled robbery leads to an innocent hero being shot dead and a hostage with a potentially life threatening medical condition being seized by two armed gunmen. It's up to Ronnie and Sam to beat the clock and find the hostage in just ten hours.