When John Briggs, a wealthy business owner, is found dead, Nikki works with forensic scientist Jack Hodgson to convince DI Gold it was murder. Leo, warned by the Home Office to rethink the Lyell Centre's operations, helps Nikki prove Briggs died from a mysterious allergic reaction. However, as suited sharks circle to buy Briggs' ailing company, Jack believes someone exploited this allergy to kill.