22d Whose, in fact, was "Chesterton's nightmare"? (5) ??M?? 1st letter possibly s
28a A native American writer (7) ??R???N
23d Provenance of Murdoch's girl (5) ??A?/ 1st letter possibly I
I don't know. The Man who was Thursday was Gabriel SYME ( no S ), and Saroyan was Armenian, but maybe I'm not understanding the subtleties of the clues.