Macintyre became interested in the topic when he found hints of Harlan during journalistic trips to Kabul, but little information remained until a lost manuscript of Harlan's planned book about his exploits surfaced. Using this as the basis and searching out related texts, Macintyre meticulously traces Harlan's transformations from sailor to "doctor" (well, he read a few medical texts) to soldier (he was a medical officer for a few months) to adventurer and king. Unfortunately, most of the excitement is left to the imagination of the reader -- Macintyre describes the situations and players with exacting detail, but rarely brings the events to life. I found myself slogging through chapters, but when I stopped at the end to review what happened, I'd realize that Harlan had again faced more stunning adventures and dangers.
I'm not sure how this book ended up on my TBR list, but I'm glad I read it, even though actually reading it wasn't nearly as much fun as I hoped. I'm clearly a very shallow person.