Altered Carbon is the first book in a series that also consists of Broken Angels and Woken Furies. I read Broken Angels some years ago on vacation, not knowing it had a previous volume, and still found it followable and interesting.
In the Altered Carbon universe, science has changed what it means to be human. One’s body is merely a possession, and one’s self resides in a machine called the cortical stack. The stack can be extracted and “resleeved” in a new body, and its contents can be transmitted across the globe, or across interstellar space, before being resleeved elsewhere. However, simultaneous multiple sleevings are a crime, for some reason.
The protagonist of Altered Carbon is Takeshi Kovacs, an Envoy. This is essentially a type of special agent employed to keep interstellar peace by overthrowing dictators and quashing terrorists. After running afoul of the Envoy Corps, and dying in a shootout, Kovacs finds himself transmitted to Earth and resleeved, courtesy of ancient billionaire Laurens Bancroft. Bancroft wishes Kovacs’ help in solving a murder: his own.
What follows is something that would be a fairly standard detective/spy thriller, were it not for the unique setting in which death is a mere inconvenience to some, an onerous expense to most, and sacred to a few. There were a few scenes where Kovacs gleefully dispensed permanent death to many, in graphic detail. I suppose it might well have been in character, and might well have been necessary to cover his tracks, but it still seemed gratuitous, in my opinion.
There is also a slight element of Fridge Horror to the setting. Considering that the brain’s functionality is made up just as much by connections and chemistry as it is by neural signals, the attachment of a device that is basically a backup tape wouldn’t quite allow one to change bodies at will. The existing neural connections would have to be completely rewired in order to host the signals properly. While that could well happen behind the scenes, the narrative doesn’t mention it.
From what the narrative does mention, I think it is more likely that the cortical stack simply treats the brain as a subprocessor, just as our own forebrains treat the more primitive parts of our own brains. The stack would have to take complete control of the brain from the time it was implanted (which happens sometime after birth) and ensure that the brain is “formatted” in such a way as to make it interchangeable with any other. Thus, in this future, humanity either evolves a silicon supercortex, or is utterly enslaved by mechanical parasites, depending on your perspective.