Intro - No Spoilers
"Palimpsest" is a time-travel story in the tradition of Poul Anderson's "Time Patrol", Fritz Leiber's "Change War", and Isaac Asimov's "The End of Eternity". And there are definite resonances with Robert Heinlein's "All you Zombies", David Gerrold's "The Man Who Folded Himself", and Chris Roberson's "Here, There, and Everywhere". I think it most closely resembles Anderson's stories, as I'll explain in detail with spoilers later. In fact, there's a reference to the "Time Patrol" series in one character's name. There are also several themes that were important in Anderson's stories here: the solitude and alienation of a temporal operative outside their own time, the moral dilemmas that result from being able to change history, and the deeper questions that need to be asked when you start wondering which history is the "real" one.
But this isn't an homage or a copy; Stross goes deeper here into these themes than Anderson did. He also spends more time and energy on the "how" of time travel, setting up a theory of physics that consistently supports the plot and the themes he's covering. Now I'm a geek when it comes to far-out theories of physics, and I'm fascinated by questions about the nature of time, and the possibility of time travel, so this is catnip for me; YMMV. But there are some twists and turns in the theory here that made me sit back and think about all the time travel stories I've read, and what their assumptions about the nature of time imply about the use and abuse of time travel. At that point, I think I've gone beyond a book review, so I'll save most of that thinking for a follow-up post, tentatively titled "On the Paraphysics of Time Travel".
In an afterward, Stross says,
"Palimpsest" really wanted to be a novel. It really, really wanted to be a novel. Maybe it will be, someday.I agree that it should be, and hope one day that it will. There are characters and settings which deserve more description and development than they have.
Here be there Spoilers
"Palimpsest" covers about as much scope in space, time, and human actions as is possible. The story begins and ends in the second person, talking to the man who is the protagonist and point of view, Pierce. In between it follows Pierce's career from recruitment into the trans-temporal organization called "Stasis", through his 20-year training, and on into active duty. Stasis' mission is to preserve the existence of humanity, despite extinction events, and in the face of the eventual evolution of the sun into a red giant that will destroy Earth. Along the way it describes, in chapters reminiscent of Olaf Stapledon's "Star Maker", several alternative histories of the Solar System (with some background on the rest of the universe). In the course of his training and work Pierce studies and helps change the course of civilizations, and helps save humanity from one of many extinctions. But in this story, that's all background; the prime mover of the plot is, ultimately, the question that Pierce must answer: who does he want to be, what history does he want for himself, the answer to which question turns out to be have a rather large bearing on the history of all humanity.
Time travel has a very SFnal problem: if you want an interesting story, you have to go beyond the science we know, and make up something. It's gotten more interesting since the 1970's with the discovery of implications in General Relativity that time travel into the past may be possible given certain extreme conditions, where before scientists were fairly certain that was impossible. There still aren't any time travel mechanisms that are known to be workable with physically feasible technology, and the ones that have been proposed are limited in range to the period of the existence of the time travel device, so writers have to either resort to some (large) amount of handwaving in describing how time travel works, or simply say, "trust me, it works, let's get to the story". Stross has chosen to describe a particular mechanism involving wormholes and singularities that isn't close to any current science, but that allows for the kinds of abilities and problems that Stasis has. It allows time travelers to change history without affecting themselves (the first task of a recruit is to kill his own grandfather before he has children), and for multiple changes to be made in a given event without the outcome of the changes to be known for certain from some viewpoints.
As always for Stross, it's not just about the hardware or action, it's about the people and how they interact on personal and political levels. Pierce has questions about how Stasis works, and what it does. Those questions get more urgent even before he finishes training, when he is sent to a primitive time on a supposedly routine cover for the extraction of another agent. Pierce is surprised to discover that he other agent is a prior instance of a former lover, an instructor at the Stasis Academy, who has not yet met him on her lifeline. Before the extraction can be completed, a multi-way firefight with advanced weapons kills Pierce several times despite frantic changes in the past of the battle, and eventually leaves him seriously injured. Are there factions in Stasis? Is there another trans-temporal organization? And why try to kill him, a lowly trainee?