Scott's subtitle is "Seventeenth-Century English Political Instability in European Context", but actually that's not really what the book is about. His argument is that all four Stuart kings (James I, Charles I, Charles II, James II) were faced with similar problems of statecraft and in fact made very similar mistakes, with the result that two were deposed (and one of those was executed). He is most interested in the intellectual reasons given by the protagonists in the struggle between the kings and their opponents (who usually controlled the House of Commons and London). In particular, he boils down the cause of the "troubles" to a) the fear of the Stuarts that their opponents were motivated by the intention of reducing the monarchy to the status of the Doge of Venice, or to abolish it altogether; and b) the fears of their opponents that the successive kings intended to introduce "Popery and arbitrary government".
The kings were certainly correct in their suspicions, as is demonstrated by the historical facts that the monarchy was in fact abolished for a decade, and restored in 1660 only by promising to restrict its freedom of action with respect to parliament (a promise broken by both Charles II and James II, which was therefore tightened up still further for William III). Scott goes into considerable detail on the political theorising of the radical republicans throughout the mid-century, both before their victory in 1648 and the reversal of that victory in 1660. I am sceptical about the usefulness of political theory in current international relations, but it seems OK to look at it as a cultural phenomenon to explain behaviour as here.
He has to plead a lot harder, and in my mind unsuccessfully, for comprehension of the radicals' fears of popery and arbitrary government, though he certainly makes it very clear that "fundamental conservatism, intolerance and anti-catholicism [were] the bases of English parliamentary policy". I'm not equipped to deal with this very neutrally, as I grew up with people marching past our house asserting that the Glorious Revolution was good for them and not for me. It has always seemed significant to me that the final straw for James II's rule came when he attempted his Declaration of Indulgence as a liberalising gesture not just for Catholics but also for Dissenters (something his brother had attempted as early as 1662). I don't claim him as a great liberal hero, but it seems ludicrous to claim his opponents as such (though some of my lefty friends do).
Scott's basic message seemed to me that these two conflicting ideas, combined with the financial and military weakness of England after Elizabeth I bankrupted the kingdom, made conflict inevitable; the Stuarts were driven to making stupid policy decisions by their own preconceptions and by the intransigence of their domestic opposition. I instinctively and deeply disagree. I suspect that the Stuarts made stupid policy decisions because they were stupid, and that better men (or women) would have made better decisions - in particular that they could have found a way of coming to terms with the domestic situation without having to depend on the good will of the King of France. William III, after all, was able to do so (and one of the best chapters shows just how contingent the 1688 invasion was on domestic Dutch politics).
So, an interesting book, but I disagreed with the main conclusion, there is very little on Ireland (where the backwash of the English troubles was particularly calamitous and horrible), and I could have survived with less on the radical political thinkers.