Hi Mary,
Shaded shells are part of the answers.
As indicated earlier in this thread, 3 of them have a single letter and 3 two letters.
Each shaded cell letter/s is derived from a book by each author. Title of the book is like a cryptic clue. For example, say one of the letters in the shaded cell was H and the title of a book by one of the authors was End of Earth, you know H belongs to that author. If that author was fourth in the perimeter, you would write H next to 4 in the bottom row.
Trick is to find the authors, find one book from each one that provides the letters in the shaded cells.
Good luck!