With their undercover assignment posing risks at every turn, Jennifer and Nick must place their trust in their handlers at the Secret Intelligence Service. Back at Homicide, their colleagues are unable to let the Supomo case rest and through their search for evidence, discover Jennifer and Nick's new assignment is a matter of national security.

When a young woman is fatally mowed down by an out-of-control car, it's thought to be a tragic accident - the driver having apparently died behind the wheel. But as evidence suggest the driver was dead hours before the accident, Allie and Duncan find themselves investigating a mysterious double homicide.