The author of the novel 'I Know This Much Is True' is Wally LAMB. He is an American author, who has written several novels and short stories. His most famous work is 'SHE's Come Undone', which was a New York Times bestseller and was adapted into a television miniseries. LAMB's other works include 'The Hour I First Believed' and 'Wishin' and Hopin''. The answer to the crossword puzzle is LAMB, which is the author's last name.