Unconquerable Sun is the first novel of the Sun Chronicles, a military space opera from Kate Elliott, one of SFF's most consistently rewarding authors over the past thirty years. Elliot started her career in space opera with the Jaran series but has become best-known for her accomplished epic fantasy series: Crown of Stars, Crossroads and Spiritwalker. Unconquerable Sun is both a genre homecoming but also an impressive historical analogue, an attempt to retell the story of Alexander the Great in a far-future, SF context.
Going into Unconquerable Sun, there were things I was expecting as normal from a Kate Elliott novel: impeccable worldbuilding that takes from a wide range of influences and merges them in original ways; excellent characterisation; richly-detailed political intrigue; and a canny and knowing sense of humour. These are all present and correct. What I wasn't quite expecting was the novel to be as foot-slammed-on-the-accelerator action-packed as it is. Elliott's always done well with battle sequences, military maneuvers and tactical elements in her prior fiction, but it's always previously felt like a secondary element, with the characters more more emphasised. Character remains foregrounded in this novel, but they are generally explored and developed whilst under fire (either on the ground or on starships). This isn't just space opera, but full-on military SF, and Elliott does it proud.
The worldbuilding is pleasingly complex, with the Chaonia Republic (here presumed to stand in for Macedonia) squashed between the Yele League (a guessed analogue for the Hellenic League of ancient Greece) and the Phene Empire (Space-Persia) and still bristling from its occupation by the Empire some decades previously. There's also the rules on interstellar travel, which can be conducted (albeit at still-achingly-slow speeds) by standard FTL engines (here called knnu drives) but mostly by beacons, fixed wormhole-gates linking systems together. Centuries previously, the beacon network suffered a catastrophic failure which destroyed most of the beacons, leaving only the periphery intact. Chaonia, Yele and Phene (among other, more distant powers) are therefore great powers still dwelling in the shadow of a vast vaster, older history, most of which was lost in the collapse. Readers keen to discern the relationship of these powers to Earth will find a few scattered clues to what happened, but not much more than that. Hopefully, this element will be explored further in later books.
Each of the major powers is also explored in depth, with the Empire being ruled not by a single ruler but a council of enigmatic "Riders," who are somehow telepathically-linked at all times (even over interstellar distances) in a way no one else understands. This gives the Empire a tremendous strategic advantage in warfare (since FTL communication is otherwise impossible) which the Chaonians hope to overturn by other means. Another key element is the space-borne civilisation of the Gatoi, who dwell on vast fleets constantly moving between the stars. The Gatoi serve the Empire as apparently-honoured mercenaries, but the Chaonians believe there may be more to this service than appears, leading to an alliance between the Queen-Marshal and a Gatoi renegade which Eirene hopes will bring the Empire down. The alliance is controversial, given it produced Princess Sun (whose legitimacy is constantly challenged because she is thus only half-Chaonian) and the long-term effectiveness of the project is in doubt. Political intrigue follows, particularly between Sun's father and House Lee, loyal servants of the Republic who are dubious of the alliance. Other worldbuilding elements feel more whimsical, such as a Chaonian reality TV show which has real power in terms of PR and politics, but is surprisingly well-developed.
On the character front, the book is told predominantly through three POVs: Princess Sun herself, through whose eyes we also get to know her retinue of allies and friends, the Companions; Persephone Lee, who tried to flee her family's smothering control five years ago to enlist in the military under an assumed identity; and Apama, a Phene pilot who is assigned to a military taskforce with a bold agenda and gradually discovers that she is far more important than anyone first suspected. Persephone tells her story in the first-person, whilst the other two stories are told in the third, an intriguing narrative device which breaks up the structure nicely (and leads to the suspicion that maybe Persephone is telling the whole story in flashback, with the other chapters being compiled from other accounts).
Unconquerable Sun is a novel of immense richness: excellent characters, terrific and detailed worldbuilding and a high concept (genderswapped Alexander the Great in spaaaace!) which in lesser hands would have been superficial but here is developed and explored in some depth. It's also a face-paced space opera with more spectacular space battles than you can shake a Star Destroyer at. Perhaps the only negatives I can consider is that perhaps a tad more build-up of the factions and players could have been accomplished before all hell breaks lose and stays loose for the rest of the book (around 150 pages into this 520-page novel), and Elliott's tendency for characters to engage in gossip, sartorial discussions and comical banter in the face of imminent death occasionally feels incongruous. That said, this isn't a book that's interested in realism more than it is in myth-making, and the feeling that you're dealing with Greek heroes transplanted in time and space makes this element more engaging.