Good short overview of the life of an important king in the last century of Anglo-Saxon England. Cnut was, with Alfred, Æthelstan, and Æthelred, one of the most important kings in the transition of England from a patchwork quilt of rival Anglo-Saxon kingdoms (the so-called heptarchy), to a single English kingdom (Wessex under Alfred), to a united England (Æthelstan's achievement), and finally to an England intimately connected to the outside world and finally subjugated by it (first by Cnut, then by William).
Ryan Lavelle's entry in the Penguin Monarchs series is a fairly straightforward, semi-academic summary of Cnut's life. I say "semi-academic" because there's a lot we don't know about Cnut's life—like where he was for years at a time, or what he was doing in Shaftesbury when he died—owing to the paucity of sources for this period. That means that a discussion of sources is necessary at some point in any attempt at a biography of Cnut.
To give you an idea of how difficult it can be to reconstruct someone's life from the available sources at this time, the Penguin Monarchs series has made the barest possible commitment to the pre-Conquest monarchy, offering only Æthelstan (r. 924-39), Æthelred (r. 978-1013, plus 1014-16), Cnut (r. 1016-35), and Edward the Confessor (r. 1042-66). For large chunks of these reigns we have only the terse entries of the Anglo-Saxon Chronicle and post-Conquest sources to go by. It's tough, but I'm glad they got in at least these four (though, as usual for the last thousand years, Harold Godwinson gets the shaft).
This treatment of Cnut is short, gives you a good sense of the complexity of his world without getting bogged down, and offers some insight into Cnut as a man. It is, however, all a bit dry, and Lavelle jumps backward and forward in time too much when explaining passing details. A bit of streamlining into a coherent narrative would have been welcome.
Still, it's a good entry in the series, especially if you want to familiarize yourself with a major figure from this period and some of what goes into the difficult and frustrating historiography of the time.
Recommended.