Avenging Angel: John Brown's Raid on Harpers Ferry 1859 (Osprey Publishing, 2012) has a very distinct contextual focus on the raid as paramilitary operation, unsurprising given its placement within Osprey's Raid series. The background is there -- Brown's prior abolitionist career, along with brief biographical information about each participant, and what they hoped to accomplish by seizing Harpers Ferry -- but the heart of the book's 80 pages is a detailed, blow-by-blow account of the raid and the armed state (Maryland and Virginia) and federal response.
Field writes clearly and well for Osprey's well honed format and the choices of illustrations and photos are solid. He's collected a large number of newspaper engravings of events surrounding the raid, with captions assessing their accuracy. The isometric maps (one depicting Brown's plan and the other the military response) offer a good picture of the town, arsenal, and relative positions of the raiders, militia, armed townspeople, and U.S. Marines. Orders of battle are a strong (or at least emphasized) element of many Osprey titles, and we see that here as well, with a comprehensive listing of militia companies involved and the aforementioned profiles of the raiders.
An interesting claim made by the author was that Brown was a keen military student, studying tactics and field fortification construction while conducting business affairs in Europe, and even commissioning a guerrilla manual written by a British military adventurer. Whatever the truth behind the degree and depth of Brown's self taught military education, the raid itself was conducted in a profoundly inept manner, the bad choices well outlined in the book.
Avenging Angel is a useful examination of Brown's Harpers Ferry operation in its military context. A systematic assessment is difficult as the actual success of the raid seemed secondary in Brown's own mind to the attempt, but Field's discussion of how it was conducted and how initial success quickly transformed into disaster does have value to students of irregular military operations.