Alys Clare 
Song of the Nightingale [EPUB ebook] 

In the latest Hawkenlye mystery, desperate men commit terrible crimes, but vengeance is on its way . . .
Winter, 1211.Former abbess Helewise moves back to her cell near Hawkenlye Abbey to help the needy, putting a strain on her relationship with Sir Josse D’Acquin, who is called to examine the bodies of three men, one of whom bears a complicated symbol carved into his chest: a symbol that signifies vengeance.
Meanwhile, far from home, Sir Josse’s son Ninian has become involved in the cause of the doomed Cathar people; soon to be swept up in a fight that they cannot hope to win