The first book of the series is titled Emperor and the setting spans the course of Pre-Roman through Post-Roman historical England with fictional protagonists cast among famous historical figures. The pace of the story is that which will suddenly jump a century or two forward between chapters, and likewise, the following two books, Conqueror and Navigator follow the same breakneck speed.
Conqueror, still set in the England, follows a new group of fictional characters and recounts the invasions of the Vikings, the Normans, and the Germanic Saxons, though not necessarily in that order.
Navigator takes the reader through the Crusades, the back-and-forth conquests of Moorish Spain and the Iberian Peninsula, and culminates with the famous sea expeditions of trying to navigate the Atlantic passage to India and the far east.
Weaver slows the pace down significantly to follow a single group of main characters, who more or less make it through the entire novel and is firmly entrenched in World War II England under Nazi occupation. In this novel, we finally meet the fellows who tamper with the history of the first three books, but I will have to say I was disillusioned with this climatic element; metaphorically speaking it was more akin a bottle rocket that fizzles in disappointment than the atomic explosion of brilliance I patiently awaited.
I might add that not having read any of Harry Turtledove's alternate history novels, I can't say how Baxter stacks against this narrow category's 800-pound gorilla. My recommendation for your typical scifi reader would be to skip this series completely. But if you're anything like me, a guy who would love to have some idea of world history but never takes the opportunity to get cracking into the dryness of textbooks, you will probably enjoy having a history lesson crammed into a novel format.