The book focuses most of its attention on Laurence's indoctrination into this strange new world (as strange, in its own way, as the culture aboard a British warship of the period seems to contemporary readers). He and Temeraire must be trained in combat, and so they are sent through combat school (albeit at a rapidly accelerated pace, as England can use all the dragons it can muster). And the book also details Laurence's growing friendship with the dragon (who can, after all, talk quite well and is very inquisitive).
The book is a rousing and entertaining fusion of historical realities with one of the most enduring mythic images. The interjection of dragons and aerial combat into the Napoleonic Wars is just bizarre enough that it works; Novik's deft development of her characters, especially that of Laurence himself, is largely responsible for this. In many respects the book seems historically accurate, and in keeping with the tradition of writers such as Patrick O'Brian. The fantasy aspects of the story are handled responsibly, and developed with a similar sense of authenticity. Were talking dragons the size of passenger jets to have existed during the Napoleonic wars, they might well have been utilized in combat in much the way Novik envisions.
His Majesty's Dragon is a deftly constructed, well-plotted "alternate history" that manages to feel original rather than cobbled together from mismatched parts (something which was a distinct possibility given the unique story elements Novik combines here). While fans of historical fiction might well chafe a bit at the insertion of mythical beasts into a historical framework where novelists are applauded for their realistic presentation of the era, Novik develops the tale with an engaging style that might well introduce some fantasy readers to the wonders of their own world's past.