Set during the Civil War, this tells the story of the Cornish families caught up in the conflict and their tangled personal loyalties. The narrative is told by Honor Harris, who has been in love with Richard Grenvile, the eponymous `hero', since she was eighteen. As this is du Maurier, we have good characterisation and atmosphere together with excellent plotting that doesn't descend into the silly or unbelievable.
However this is a book which is far weaker than DM's classics such as Rebecca. There is very little attempt to recreate historical atmosphere and though this is supposedly set in the 1640s onwards, it reads as a modern book (written 1946). However the shortfalls are redeemed by the strength of the central portrait of Grenvile and his relationship to Honor (in both senses). Both ruthless and charming, cold and passionate, bitter and vengeful while unremittingly loyal to the king and the monarchy, Grenvile towers over this book as a huge creation. We might not like him (and `like' is far too weak a word to use for him) but then neither does Honor, although she does love him to the end. And it is this ambiguity and complexity which gives the novel its strength.
So don't read this if you want dashing, romantic sentimentalism: du Maurier is far too astute a writer than that. But for something much more akin to Heathcliffe in a political setting this is highly recommended.