Whenever I want a guaranteed great read, I turn to Georgette Heyer. I've read this novel several times, and it's one of my favourites of hers. The humour is brilliant, the characters are well-drawn (I particularly love the foppish Claud and his venomous-witted brother Vincent), the setting on the Sussex marshes is eery, and the resolution of the plot is both over-the-top and masterly at the same time. I would give it 5 stars if the heroine were a bit less passive (unusual to have such a passive heroine in a Heyer novel. I'm reading Faro's Daughter next, to remind myself how strong her female leads usually are.)
If you've never read any Georgette Heyer, I envy you. You're in for a great treat.