Share this Page Clifford Riley 1 Total Resources 1 Books Books by Clifford Riley 1 Sort by Number of Resources Number of Awards Book Title Year Published Word Count Reading Level: ATOS® Reading Level: Lexile® Add Multiple Titles to Reading List Browse books by Clifford Riley Operation Trinity by Clifford Riley 3 Resources Add to Reading List Share this Book Series by Clifford Riley1 The 39 Clues Series Share this Series Images courtesy of publishers, organizations, and sometimes their Twitter handles.