When a thirteen stows away on a Mars-to-Earth shuttle--methodically butchering and eating everyone else on board over the long flight home--a thirteen bounty hunter is called in to track him down. This leads to plenty of fighting, international politics, a little sex, a lot of murder mystery, abundant future-style bigotry, and the long slow unwinding of a complex conspiracy.
Morgan spent a lot of time hammering at the differences between humans and thirteens. Like, A LOT of time. I think he felt compelled to do so because it didn't hold water very well. The concept is interesting--übermales bred out of the species during the transition from hunter-gatherer to agriculture--but he founded it on a lot of weird assumptions about masculinity/femininity. Embracing negotiation, group cooperation, NOT leaping to join the army...these things don't strike me as strict functions of femininity, they're just functions of having more options and opportunities due to the stability and wealth provided by farming. This constant harping on how very alien thirteens are psychologically was tiring. The thirteen hero keeps acting like a standard-issue tough guy, then tossing out a comment about he's "wired" for it.
Aside from that repetitive annoyance, Thirteen was terrific. It has a sprawling but logical conspiracy, a wonderfully detailed and logical future political landscape, three-dimensional characters with complex and believable motivations, and plenty of surprises. The US has splintered into three nations, the wealthy and tech-savvy Pacific Rim, the liberal and powerful UNGLA in the northeast, and "Jesusland", the poor backward states in between. This allows Morgan to look at modern issues like immigration and abortion through fresh eyes. These aren't big plot points by any stretch, they just give the story more punch.
Not quite as good as Altered Carbon but still a top-notch read.