Mur Lafferty’s Six Wakes opens with the single best locked-room mystery you’ll read this year. Maria Arena is a crewmember aboard the Dormire, an interstellar colony vessel. The Dormire is crewed by six people who will remain awake throughout the years-long journey. The idea is simple: As each crewmember ages and finally dies, they will be downloaded into a freshly grown clone body, with all the skills and memories they’ve acquired over their previous life downloaded from the mind map of each person kept by the ship’s computer. The system’s worked for decades—cloning has revolutionized culture on Earth and it’s a perfect way to maintain a crew’s presence on the Dormire’s voyage humanely (and without going all horrifically stalker-y like Passengers did).

Or at least, that’s the theory.

The reality is that Maria wakes up in a pod streaked with blood. As she and her colleagues slowly come to, they realize that something terrible has happened. The entire previous generation of the crew are dead, murdered by one of their own. They have no mind map for what happened, only the sure knowledge that one of them, and perhaps more than one, is a killer.

With the Dormire in bad shape, Maria and her colleagues must repair the vessel, save the mission, and discover which of them is the murderer. But as the investigation deepens, it becomes clear that each member of the crew has very different, very dark reasons for taking the voyage…

The genius of Six Wakes is all in the pacing. As Maria—who’s a remarkably positive and friendly protagonist—and her colleagues get on with their latest lives, it becomes apparent that the book actually has three different sides to it, all unfolding at once. The first is the locked-room mystery in space, which nails the amazingly difficult problem of unfolding at the right pace; you get just enough hints as the investigation progresses, each chapter slowly needling the characters and plots alike so we never forget it’s there. The comforting routine of life on the Dormire is contrasted with the constant, visceral realisation that one of these likeable, relatable people is a multiple murderer. In the immortal words of The Thing, nobody trusts anybody now and they’re all increasingly tired.

That leads to the second main aspect of Six Wakes, as it serves up a fascinating variety of character studies. We get backstories and additional context for everyone on the Dormire, flashing back to their original lives before the Dormire. In each case, there are some major surprises, and some remarkably dark turns waiting for you. Hiro in particular has an elaborately designed knife-twist of a past that grows more horrifying the longer you ruminate on it. Likewise Wolfgang, the ship’s dourly competent Chief of Security. In each instance, the reason for the characters’ behavior in the present is uncovered in the past. In an even smarter narrative turn, these flashbacks also provide reasons for each character’s journey on the Dormire and the surprising common ground they all share. Sallie Mignon, billionaire and venture capitalist and the muscle behind the mission, interacts with each character in very different ways. She’s the invisible puppet mistress, the seventh crew member, whose agenda is never directly revealed. Instead, Sallie acts as the power behind the flight console, the woman whose ideas have pushed this ship out into space and these seven people into close proximity. The end result is a phenomenally clever mosaic portrayal of a character who isn’t quite a villain or a heroine, but rather the embodiment of change, with all the amorality that implies. Lafferty has talked about a possible sequel to the novel and there’s boundless possibilities in that idea. But, for me, I want more of Sallie (if only so that we can keep an eye on her…)

And that leads us to the third element of the novel: the discussion of cloning itself. What Lafferty has done here is fiercely clever and very subtle, folding a roundtable discussion about the ethics of human cloning into the lives of her characters. One of them is the victim of its very worst excesses, another one of its architects, and a third has defined themselves against it in an understandable but profoundly brutal way. In every case, these characters embody not only a single viewpoint but a constantly shifting one—as you find out more about them, your attitude towards cloning as it’s presented here changes. As they learn more about what’s happened, their attitude shifts, too. It’s a subtle, character-driven way of exploring every side of the central issue of the novel, and it’s done with a level of grace and perception that is rare, in my experience. Even better, in constructing her story in this way, Lafferty creates a complexly interwoven and self-supporting narrative: The clones learn about themselves and their pasts, we learn about both, and all of that provides a foundation for the hunt for the murderer and the unavoidable consequences of the investigation.

Six Wakes is an extraordinarily clever novel, one that grows even more so the longer you’re able to sit and think about it. The central crime plot is expertly designed and played out, the characters are complex, realistic, and mutable, and the atmosphere is never more than a few pages away from nail-biting tension. And on top of all that, this microcosm of recycled humanity is a petri dish that Lafferty uses to examine just what it means to live forever. For some, that leads to horrific degradation and crime; for others, it leads to their best selves. For all, it leads to a gripping story, brilliant characters, and the most fundamentally satisfying exploration of a big idea you’ll see this year: It’s unmissable.

Alasdair Stuart is a freelancer writer, RPG writer and podcaster. He owns Escape Artists, who publish the short fiction podcasts Escape Pod, Pseudopod, Podcastle, Cast of Wonders, and the magazine Mothership Zeta. He blogs enthusiastically about pop culture, cooking and exercise at Alasdairstuart.com, and tweets @AlasdairStuart.