It's 1738 and Silence Hollingbrook, a widow, works with her brother Winter running the Home for Unfortunate Infants and Foundling Children in the dangerous St. Giles section of London. Shortly after her husband William was lost at sea, someone left an infant on her doorstep, and she has treated the little girl as her own, naming her Mary Darling.
One day Mary Darling disappears and Silence tracks her to the "palace" of notorious river pirate Charming Mickey O'Connor. Charming Mickey was responsible for ruining Silence's reputation (and marriage), even though he never laid a hand on her. (See Wicked Intentions (Maiden Lane #1). Silence hates and fears Mickey but she nevertheless faces him down and demands the return of Mary Darling. Mickey announces that Mary Darling is his daughter, that she is in danger from his enemies, and that Silence can continue to take care of her only is she lives in Mickey's palace until the danger is passed. Silence reluctantly agrees.
The rest of the story takes us from the initial antagonism to growing affection between Mickey and Silence. The lurking danger from Mickey's enemy, the so-called Vicar of Whitechapel, is a constant presence. Of course, there's an HEA, but the adventure leading up to it is among the best I've seen in a romance novel.
Silence is a strong heroine and not the least bit missish. Charming Mickey is the ultimate bad boy charmer; I'd have to rank him up there with Lisa Kleypas's Derek Craven (and if you haven't read Dreaming of You, what are you waiting for?), and indeed he shares some of the same traits -- a horrible childhood, a compulsion to make more and more money, and a willingness to face death to protect the woman he loves.
I disliked Wicked Intentions and skipped Notorious Pleasures (Maiden Lane #2). This book was so good though that I'll probably go back and read it while impatiently awaiting the release of Thief of Shadows (Maiden Lane #4).