His Majesty's Dragon takes place in an alternate history where dragons are real and have been put to work as the military's answer to air service. They're intelligent creatures, depending on the breed, and speak and understand. They can be quite large too, again depending on the breed, and can carry a captain and large crew on missions for surveillance, offense, or defense.
His Majesty's Dragon takes place in the time of Napoleon and his attempt to take England from across the channel. This book follows the tale of Temeraire, a dragon who's egg was captured from the French and hatched aboard a British ship. That ship's captain was chosen by the dragon to be his rider and the story unwinds from there. I really enjoyed this book and intend to follow up with others by the author. Highly recommended.