Worlds of the Timestream: The Interregnum Series, Book 5: The Nexus By Richard J. Sutcliffe

The Timestream is at least six known versions of Planet Earth arranged in hexagonal fashion. Each has different histories and societies, some different geologies, but all share the same physical laws and chronology. At critical historical points on one of the planets, crucial decisions result in two Earths with the same prior history but differing subsequent ones. Major events on neighbouring planets in the Timestream affect each other strongly...

The sensational trial over which Tad O'Kelly presided as Senchus is now over. Mara Meathe tackles a multitude of foreign assignments, battling pirates, gun runners, kidnappers, and a host of plots against the realm.
Elbon, the Builder of Meta, returns from a meeting of the elders to Tirdia and the orphanage at Berea, unaware his daughter Eider has followed him. She encounters Lucas and the two have a narrow brush with gangster Al Marcotti's thugs. In the aftermath, Lucas eavesdrops on Eider's conversation with her father and hears of their relationship and of the other earths. His loyalties now torn, Lucas leaves that afternoon's creation debate to strike out on his own. But Eider follows, and the two are caught up in both a world-dividing nexus and a Marcotti kidnapping.
Royal Army officer Maeve Derry sends one of her Centralia cadets out on a training mission only to have to pull his body from the bottom of a river several hours later. What she then learns necessitates the reappointment of Tad as Senchus. Another sensational hearing at Tara ensues and is punctuated by a shocking and cowardly attack. After Maeve's return to Centralia, she finds herself lured to the St. Charles Islands, where she disappears.
Clan MacCarthy forces mount an all-out attack only to come under pressure themselves from the Friends at other locations.