“No platform for racists!” shouts a crowd of protestors, interrupting the controversial lecture of American academic Paul Yelland (David Soul), a guest of Oxford’s Department of Criminology. An anti-racist extremist hurls a threat at the professor, and later that night, Yelland is discovered strangled to death with a noose made from his own tie. The investigation draws Inspector Lewis (Kevin Whately) and Hathaway (Laurence Fox) into a criminology department rife with murder suspects, many of them already guilty of lesser crimes.