Due to the actions of the High Ridge government in War of Honor, which led to a successful attack on key Alliance shipyards by the Republic of Haven, the Star Kingdom of Manticore finds itself decidedly on the short end of the strategic balance between the two warring star nations. Admiral Honor Harrington is placed in command of Eighth Fleet, the Manticoran Alliance's primary offensive force, which is the sole heavy formation available for operations against Haven. Queen Elizabeth and her senior advisors project it will be at least two "T-years" (Earth years) before they can expect any significant numbers of new construction to begin bolstering their thin wall of battle; this while Haven's progress under Admirals Theisman and Foraker have given them an even larger force advantage, and smaller technological disparity, than Haven suffered before the beginning of hostilities in Short Victorious War.
Strategically, the goal of Honor and Eighth Fleet is to instill enough operational caution and sensitivity to losses in Haven to force redeployments; this would have the desperately needed effect of reducing the available number of ships of the wall Haven would then be able to concentrate for offensive action against the Star Kingdom and its allies. Despite the grave circumstances, the Star Kingdom finds itself spread dangerously thin against its security commitments; to itself and the Alliance. At All Costs climaxes with the largest and most critical battle of the entire series, as Havenite forces attack the Manticoran home star system.
Honor continues to work closely with Hamish Alexander, now First Lord of the Admiralty, on the military and political challenges facing the Alliance. Their professional respect for each others' abilities, and their need for mutual support as they navigate the precarious political landscape in the Star Kingdom, has led them into the very romantic embrace the High Ridge government tried to insinuate during War of Honor. While this is not the dire political crisis it was during the prior Star Kingdom government, it still offers numerous personal and professional difficulties for them. Unfortunately, they find themselves trapped between their emotions and their responsibilities to each other, to the loved ones in their lives, and to the Star Kingdom and the Alliance.
Most of the action takes place simultaneously with the events of The Shadow of Saganami. In addition to Manticore, Haven, and Grayson, front stage players (even those lurking in the wings of the stage) now include the Andermani, which have entered the Manticorian Alliance; the genetic slavers of Mesa, secretly striving to keep Manticore and Haven shooting at each other as long as possible; non-self absorbed elements of the Solarian League continuing the inexorable and glacier creep of League influence; and the inhabitants of the Talbot Cluster, clamoring for membership in the Star Kingdom after discovering the new Manticore Junction terminus in their region of space.
The book was released in hardcover in 2005 (with a CD-ROM containing free copies of other works written by Weber). Advanced Reader Copies were made available for sale at baen.com some months previously, with a sizable portion of the book being 'snippetted' on Baen's Bar for free.
Author David Weber has stated that he intended many of the events of this book to end differently and have this book end the initial story, the second part would begin in another 20 years as a new generation ages. With the introduction of Mesa and the Solarian League issues, many plot elements intended for the new series remove the need to add a new generation.
David Weber has stated his original plan was to have Honor in charge of the 3rd fleet during the final battle, and perish during the battle. Her son, then would have had his own series start as he came of age, at which point the Solarian League begins its break up, and a long war begins.