It’s been some time since folks last saw the actor reprise his role as Leroy Jethro Gibbs on NCIS in November. While viewers know he narrates NCIS: Origins, it does lead us to wonder something major: What else does Mark have in the works?
As it turns out, the actor is going from the screen to the world of literature. In January 2026, Mark announced that he had teamed up with retired NCIS special agent Leon Carroll Jr. to write a new book, Ghosts of Sicily: The True Story of the Naval Intelligence Agents Who Courted the Mob to Fight Nazis in America and the Battlefields of Italy. And even though the news broke earlier this year, folks may be surprised to learn that it won’t be long before they can pick up a copy.
As People announced at the time, Ghosts of Sicily will debut on April 14, 2026. What’s more, Mark had something to say about what fans can expect from his latest work.
“Ghosts of Sicily” by Mark Harmon and Leon Carroll Jr.
“The history of World War II has always been fascinating to me, and there have been many books written,” he shared at the time. “The Office of Naval Intelligence/ONI played a huge part in the invasion and new details uncovered a riveting, complex story. All records were burned after WWII. Why? Read Ghosts of Sicily and find out.”
According to the book’s announcement on Publishers’ Weekly, the book will follow the true story of how the Office of Naval Intelligence “used gangsters who ran New York City’s waterfront as intelligence assets.” And while the initial operation didn’t necessarily prove effective, it did have a lasting impact on future missions carried out by Naval Intelligence in Italy.
Ghosts of Sicily is actually the second time Mark and Leon have teamed up to write a literary work. Fans may remember that the duo first worked together in November 2023, when they published Ghosts of Honolulu: A Japanese Spy, A Japanese American Spy Hunter, and the Untold Story of Pearl Harbor.