Agatha Raisin and the Wizard of Evesham by M.C. Beaton

Agatha Raisin and the Wizard of Evesham (Agatha Raisin Mysteries, No. 8) - Agatha goes to a new hairdresser, Mr. John, who is a wiz with hair.  She suspects he is blackmailing his rich women clients.  While she is investigating his house is torched and John is murdered.