1Ac 4 letters. An alternative spelling of AMICE. Also an author's name. You fit it by looking at your solutions to 2d, 3d, 4d.
Once you have the theme (Google the Title), you might start to see how the top half of the grid must pan out. There is a thematic missing item. A 6 letter word which fits at the top of column 3 (but not top shaded row). It goes to make other real words in 9Ac, 11Ac, 15Ac, 18Ac, 21Ac. Good luck with the rest. I'm still struggling.