The measure of a novel based on a television series is whether or not the characters say and act as they would on the show and this book does pass that test very handily. The dialogue between Callan and Hanna is spot on for the banter they exchange in the series and the same goes for the other field agents, Kensi and Deeks. The story, involving the murder of a retired admiral, a captured German U-Boat at the end of World War II, and a terrorist plot against Los Angeles moves along quickly, alternating between the terrorists and the NCIS investigation.
The only negative, and it's a small one, is I found the subplot of Deeks using animal urine for a cologne to be totally unnecessary and a distraction. Perhaps it was for comedy relief? Not sure. One other note before I highly recommend this book to fans of the show: if you aren't up to date with the show at the time this book was written, there are spoilers about what happens on the series.