I found the book interesting and a worthwhile read for anyone with an interest in the origins of Scotland. The main difficulty for any historian, writing of the time and place, is obviously the paucity of information. Needless to say, the available sources do not always agree, and bridging the gaps requires some very tenuous assumptions to be made. In addition, the historian has to decide whether his primary objective is to present a broad trail of alternative scenarios, paying full attention to the strengths and weaknesses of his evidence, or to go for a tighter narrative, pausing only to indicate the points about which there are greatest doubts. In this case there is switching between the two, with the narrative gaining strength in the late chapters, even although the quality of the evidence seems no higher. Perhaps a timeline, indicating events like battles, along with the reigns of the most significant kings would have helped the early chapters. I also would have liked a less cautious approach to the general maps to include some of the author's best judgements as to locations.
I will make two specific points; firstly the author appears to believe that the disappearance of Strathclyde in the 11th century, was accompanied by the removal of the top slice of its society, replaced by its Gaelic, Scots equivalent and that this percolated very quickly through society. Presumably, this would also be his model for the Pict/Scots transition in the 9th/10th centuries. Secondly, the author appears to favour strongly the English interpretation of the allegiance question, with Kings of Alba and its successor states, really just sub-kings from the reign of Athelstan of Wessex onwards to the 12th century.