American academic Paul Yelland faces accusations of racism when he presents his theory on Criminal Dangerousness to an Oxford college and is later found murdered. Married professors Anne and Robert Fraser claim they invited him to raise their department's profile and Robert,who is having an affair with student Nina, points Lewis towards Myra Bennett's anti-fascist group. Yelland also dealt in antiques and had angered two clients with a forgery and furthermore turned out to be the father of a staff member,whose mother he deserted when pregnant. Then Nina is killed after Anne has discovered the affair. Lewis must not only expose a killer whose motive goes back many years but battle with tooth-ache in the light of his fear of dentists.