If you desire to be one of those Baha'is who can tell the stories of the Central Figures, here is a clear, and easily readable account of the life of the Bab. It can be used as an intermediate step that will expand upon and strengthen what you have already learned in Part 2 of Ruhi Book 4. It is also an excellent introduction for new inquirers.
Hour of the Dawn: The Life of the Bab
The 221 pages in Hour of Dawn may seem short to some people. For me it was packed full of information and very straightforward and lucid in tracking the life of the Blessed Báb. I have read other books about His life but this one clarified the timeline of the dramatic events surrounding His ministry and His travels. This is a wonderful book to read during the holy year which marks the 200th anniversary of His birth.