Mark Harmon may be best known for his role as Leroy Jethro Gibbs on NCIS, but he’s now turning his attention to writing.
In January 2026, Harmon revealed that he has teamed up once again with retired NCIS agent Leon Carroll Jr. to co-author a new book titled Ghosts of Sicily: The True Story of the Naval Intelligence Agents Who Courted the Mob to Fight Nazis. The book is set for release on April 14, 2026.
The story explores a little-known chapter of World War II, focusing on how the Office of Naval Intelligence used organized cr1me figures in New York as intelligence assets. While the operation had mixed results, it ultimately influenced future missions during the war in Italy.
Harmon shared that his interest in World War II history inspired the project, noting that newly uncovered details reveal a complex and compelling story. He also hinted at unanswered questions surrounding the destruction of records after the war.
This marks the second collaboration between Harmon and Carroll, following their 2023 release Ghosts of Honolulu, which also explored real-life intelligence operations.
While fans continue to hope for more on-screen appearances from Harmon within the NCIS franchise, his latest project shows he remains deeply connected to the world of naval intelligence—this time through storytelling on the page.