The Secret Fear by Barbara Cartland is the story of Arabella, who is sent to live in the house of the Marquis of Meridale and care for a child who lives there. The Marquis is off fighting the Napoleonic Wars and a local highwayman is using his house as a cover. When the marquis returns, he is intrigued with Arabella, but other issues interfere before they can fall in love!
The Arrow (UK) cover is less menacing, but very pretty. Our heroine is lovely in a pink gown with a bonnet in her lap. Her hair is loose, which would be unusual. She sits in a phaeton with the hero and we see a groom standing on the back. The hero holds the reins loosely while he converses with the heroine. Click on the pictures to enlarge.
Update: Reader Tracey J reminded me that there was an old hardcover of this title with a different cover which I believe is also another Francis Marshall and am adding it today! Thanks, Tracey!!