The Duchess Contract by Samantha Hastings

Miss Selina Stubbs signs the contract of her life with her father—her perfumes in every major shop in London, in exchange for marrying the reluctant son of the Duke of Hampford.

Lord Theophilus, the courtesy Marquess of Cheswick, has no desire to wed the daughter of a London merchant. He wishes to go to Africa and study the animals there. But his father, the Duke of Hampford, desperately needs her dowry.
After the wedding, Selina gets to know Theophilus and learns of his care for wounded animals. Together they plan a daring rescue of a lion from the Tower of London. Selina decides to make a new bargain…this time for love.