This is Barry Eisler's first novel outside of the John Rain assassin series (although this book takes place in the same "fictional universe," and one character from this novel later appears in a John Rain novel).
Obsidian is encryption software, and the author/programmer is trying to patent it... but now he's dead, someone at the patent office is dead, and Bay Area attorney Alex Treven is afraid he might be next.
Fortunately, Alex's brother Ben is in the Army, and knows something about guns and fighting. (Alex doesn't know it, but Ben is actually an assassin for a shadowy U.S. agency.) Unfortunately, the two have barely spoken to each other for years, bitter over problems in their family.
As the plot expands, the brothers struggle to understand why Obsidian is worth killing over, why Russians are interested, how does a song fit in, and whether they can trust the beautiful Iranian associate attorney or the well-connected senior partner?
This novel features a blend of action, family problems, and even a romantic triangle. I had trouble "getting into" the novel at first, found both brothers initially unappealing, and the "troubled family" subplot never engaged me. Ben also worries about whether his "assassin" work has replaced his former self, and does some self-examination that, again, didn't work for me. These flaws were a disappointment, as this is an author whose characters and stories have greatly entertained me previously.
The novel features some combat violence and some sexual content (not too explicit). One thing that annoyed me - and it seems to be a feature in recent novels by several authors - is the characters' self-dialogue about masturbation. All three major characters mention it! For me, that's "too much information" and I really don't want to know...
Nevertheless, the novel isn't bad, has some twists, and comes to a satisfying conclusion. The plot could be used for a wargaming campaign, but would need to be adjusted to include more combat.