The Age of Treachery — Gavin Scott

It is the winter of 1946, and after years of war, ex-Special Operations Executive agent Duncan Forrester is back at his Oxford college as a junior Ancient History Fellow. But his peace is shattered when a much-disliked Fellow is found dead in the quad, stabbed and pushed from an upper window. A don is suspected and arrested for the murder, but Forrester is not convinced of his friend's guilt. On the hunt for the true killer, he finds himself plunged into a mystery involving lost Viking sagas, Satanic rituals and wartime espionage.