Rod Bennett's The Apostasy That Wasn't: The Extraordinary Story of the Unbreakable Early Church is sure to be one of the best-written histories you will ever encounter. Bennett is an astonishingly talented writer, and he successfully brings to life the most tumultuous period in Church history. If you understand the importance of the Council of Nicea, but remain fuzzy on the build-up, key players, and immediate aftermath, then this your guide.
The book's title actually does double-duty. In terms of apologetics it answers the popular (but erroneous) charge that Christianity was corrupted at the time of Constantine, and Christ's simple, straight-forward Gospel was shot through with elements of paganism and stood in need of reclamation (via the Reformation, Joseph Smith, Charles Taze Russell, etc.). In terms of Christian history, however, the book's title captures the way that Antony of Coma, Athanasius, Pope St. Julius I, Basil the Great, Gregory of Nazianzen, and others fought and overcame the most dangerous, far-reaching, successful heresy ever faced by the Church - Arianism.
Bennett zeroes in on the most important actors, with Athanasius as the book's main protagonist, and provides enough back story to bring the second and third centuries to life. Dramatized vignettes may seem out of place in a work of history, but Bennett uses them sparingly and in a way that breathes life into historical characters. A lesser writer couldn't pull it off, but Bennett hits the mark. His vivid prose draws you into the action, and you remain there when he transitions back to narrating the history. (On a personal note, after reading Bennett, I can finally keep my Eusebiuses straight.)
The Apostasy That Wasn't is exceptional.