Ethan Urquhart is a doctor on the all-male planet of Athos, which is reliant on important genetic cultures in order to increase their population. When the latest culture shipment is contaminated and destroyed, Ethan is dispatched by his government to the transfer point at Kline Station to investigate. Almost immediately after his arrival, Ethan is drawn into a web of intrigue and conspiracies featuring agents from the Cetagandan Empire and the unnerving (for Ethan) presence of a female intelligence agent from the Dendarii mercenaries.
Ethan of Athos is, chronologically, the sixth novel in the Vorkosigan Saga, although it was the third to be written. Even more confusingly, it is often omitted from counts of the series due to the total non-appearance of the series' main character, Miles Vorkosigan. However, Ellie Quinn, who appeared briefly in The Warrior's Apprentice and goes on to make more important appearances alongside Miles later on, plays a major role and this book establishes a fair bit of her character and backstory. So my recommendation is to accept it as part of the saga and move on.
I enjoyed Ethan of Athos a lot. It's what Bujold does best, a comedy-of-manners romp taking in scheming, intrigue, wheels-within-wheels, deceptions and double-bluffs, and a thin layering of real science (a more thorough exploration of the uterine replicator technology mentioned in previous books) and social commentary on top. There's some nice character scenes and moments of humour, and Bujold writers her typical wit.
However, the book feels like a somewhat missed opportunity. There are a few SF novels which take a look at societies where either women are put in charge or are dominant (such as David Brin's Glory Season), or where the normal genders don't exist as we know them (obviously, The Left Hand of Darkness), but surprisingly few about the idea of a planet where only men exist. The early and closing chapters set on Athos show that Bujold has put a lot of thought into this idea and how it works, and the resulting commentary it offers up on male gender roles is facinating. But as a concept it only bookends the novel, the bulk of which is a more basic - if still fun - SF thriller.
Ethan of Athos (***½) is a solid, enjoyable SF novel, but one that feels like it could have been a lot more than that if the story had remained on Athos for its duration. Otherwise, this is a reasonable addition to the Vorkosigan series. The novel is available now in the UK and USA as part of the Miles, Mystery and Mayhem omnibus.