The first is a long overdue biography of Rigdon. He is best known among Mormons for his pivotal role in the early days of the church and was in the First Presidency right up until Joseph Smith's murder. After that he tried to assert his claim to the presidency and when Brigham Young and the apostles supplanted him and other claimants he went his own way and was excommunicated by Young for continuing to try to regain his former leadership role. Like so many early leaders of the church he became an apostate cast by the wayside and largely forgotten.
Most interesting to me was his religious exploits after Smith's death because I think it gives great insight into how to consider his involvement in the founding of Mormonism. After to failing to gain a following in Nauvoo he head east to Pittsburgh (?) and took over leadership of a branch of the church there. He became a prophet and tried to establish a new Zion in a similar fashion to what he had done with Smith in Kirtland, Independence, and Nauvoo. Like those previous attempts he failed miserably. He finally wound up living in impoverished circumstances with his son's family. His son forbid people from discussing religion with his father because of the problems it caused.
Apparently in secret, Rigdon continued to act as a prophet to people who he led via letters as he remotely led them from site to site of new Zions while constantly berating them with prophecies condemning them for failing to adequately support him. His small flock apparently placed great faith in him as they sacrificed everything trying to support him and comply with his arbitrary directions.
In a tragic turn of events for seekers after truth, Rigdon's wife apparently burned all of his papers. One wonders what might have been in that treasure trove that he didn't want exposed to the world but we'll never know.
The second book explores the possibility that Rigdon had a role in the production of the Book of Mormon. Despite the length of the book, there is really no solid evidence. About all that can be said is that they have shown that Rigdon was in the right places at the right times so that it's a possibility. But is is so highly speculative in nature that the case is hardly compelling. It can't be ruled out, but then again neither can the theories proposed by Brody and others including B.H. Roberts who concluded that Smith was certainly capable of producing the Book of Mormon on his own using the resources at his disposal.
But, when you take the two books together it struck me how quickly Smith's prophetic voice changed as soon as he joined with Rigdon in Kirtland, Ohio. Nearly all of the church's revelations were given in Kirtland with Rigdon by Smith's side the whole time. Prior to Smith, Rigdon had already spent years developing his own Christian restorationist theology as a Cambellite minister and had had a falling out with the Cambellites because he seemed to go to far. However as soon as he linked up with the Mormons you can see his ideas finding fruit in Smith's revelations. During this period, not only were most of the revelations given, but he and Smith "translated" the Bible, established Zion in Missouri, and tried to set up a communal order and various business enterprises. It is easy to understand why so many people at that time believed that Rigdon was the real founder of Mormonism.
Like Smith, Rigdon was never successful in earning an honest living with his own hands and relied on his religious roles and the charity of others to support himself. After his split from the main branch of Mormonism it becomes easy to see him continue a pattern until his death where he tried to use the faith of others to his own advantage.
I highly recommend the first book, but not the second unless you really, really want to see how far people are willing to stretch scanty evidence or are very interested in minute details of the period.
Oh. The second book also raises a very good point about how very little we know about Oliver Cowdery prior to his role in the production of the Book of Mormon and the founding of the Mormon church. I've pointed this out with regard to the testimonies of the three witnesses, but it is extremely suspicious how little we know of Cowdery's life. As church historian it makes one wonder at what he might have been trying to hide and the book actually does a pretty good job at pointing out what some of those things might me.
Smith and Rigdon were the key figures in the foundation of Mormonism and it's theological evolution. I think that the character of Smith's closest associate sheds a great deal of light on Smith himself.