The novel that everybody recommends and nobody quite expects. Lost Stars is shelved as young-adult, marketed as a Force Awakens tie-in, and is in practice the most emotionally serious book published under the new canon.
The structure
Ciena Ree and Thane Kyrell grow up on Jelucan, on opposite sides of a caste line, obsessed with flying. Both are accepted into the Imperial Academy. Then the original trilogy happens around them, and the two of them end up on different sides of it — not through a dramatic conversion, but through a long accumulation of things each of them can and cannot live with.
Gray runs the whole original trilogy through this lens. Alderaan, Hoth, Endor, and finally Jakku are all seen from inside cockpits and briefing rooms belonging to people we know. It is the single most effective use of familiar events in Star Wars fiction, because the events are not the story — they are the pressure.
Why the Empire question works
Most Star Wars fiction treats service to the Empire as either villainy or a mistake awaiting correction. Gray refuses both. Ciena's loyalty is built out of honour codes, family expectation, an oath she takes seriously, and a genuine belief that order is worth something — and the novel makes those things sympathetic without ever suggesting they are correct. When Alderaan is destroyed, we watch her build the rationalisation in real time. It is the best passage in the book and it is horrifying.
Thane
Slightly the weaker half, because his path is the expected one. Gray compensates by making his defection unheroic: he leaves out of disgust and drifts into the Rebellion by degrees, mostly because he has nowhere else to be. There is no speech. There is no moment. That is the point.
The romance
Central, and handled well. This is a love story in which both parties are right about the other and wrong about everything else, and Gray has the discipline to keep them apart for most of the page count. Readers allergic to romance plots should still read this one; readers who came for the romance will find it earns its ending.
Craft
Gray's prose is clean and unshowy, and her structural control is exceptional — the novel covers roughly twenty years and never once feels like a synopsis. The flying sequences are the weakest writing; the quiet institutional scenes are the strongest. She is far more interested in what a chain of command does to people than in what a TIE fighter does in a turn.
Where it sits
It is also, incidentally, the most detailed account in canon of the Battle of Jakku, which matters if you are reading toward Aftermath or the sequel films. But do not read it for continuity. Read it because it is good.
Who should read it
Everyone, including people who do not like Star Wars. It requires having seen the original trilogy and nothing else. If you are building a shelf of five canon novels, this is the first one on it.