Most people who pick up this book will already have read some of the travelogues of the "mad dogs and Englishmen" who wandered through Central Asia in the 19th and early 20th century: Burnaby and Nazaroff's memoirs, as well as any of Peter Hopkirk's books on the era.
But here we have a real fish out of water story, and a fascinating one at that: an American Quaker leading, or joining, armies through Afghanistan and elsewhere in the name of, variously: the sitting ruler of Afghanistan, the deposed predecessor, his Sikh neighbor, the British Empire, and arguably himself as "Prince of Ghor."
The tale is fascinating because it's so poorly-known, despite the fact that Kipling's fiction, which I understand to be inspired by Harlan and other adventurers of the time, is so well-known.
Undoubtedly, Harlan's own financial misfortune and quiet death contributed to the obscurity of the narrative, but Macintyre does a great job of weaving the scraps together, and keeping the story's pace. An interesting read, and a bit of history which has earned its place in Central Asian lore.