You mean the English Civil War? I got interested for a while in the Scottish side of that, and if you're interested in that you could check out James Graham, 1st Marquis of Montrose, who was quite a guy! The most authoritative book about him is still the one by Ted Cowan, 'Montrose: For Covenant and King', first published 1977 but republished with revisions 1995. God that makes me feel old.

For Scotland... depends on what interests you? If you're interested in wars, try Geoffrey Barrow's 'Robert Bruce and the Community of the Realm of Scotland' (3rd edition) - it's one of the most readable academic history books I've ever come across and deals with the 1st War of Independence.