SOLVED. Historical romance - Hero is a spy who investigates a smuggling ring at the heroine's family mansion [s]

[Morgane]

The story takes place in England (possibly in the Victorian era).
The hero is a lord, and secretly a spy. He needs to go to some house party in the countryside in order to investigate a possible smuggling ring. His father is/was an English lord, and his mother was Indian (his father travelled to India, and the hero spent his first years there).
The heroine is not the prettiest girl (I think she has a much prettier younger sister, but I might confuse a few books together...), so I think she has given up on marriage. I am not sure, but I think I remember her mother likes her sister much better, and wants the lord for the heroine's sister.
There is one scene where the heroine is in the library, reading a book about sexual positions (since she thinks she will never get married, she thinks it's the only way she will ever find out about sex), and the hero finds her there. She tries to hide the book, then goes to bed, but the hero eventually finds the book, and he is surprised to realize that the quiet spinster was reading a sexy book. When the heroine goes back to get her book, she sees that the hero is still in the library, and he "confronts" her about wanting to know about sex, then kisses her. I don't remember if they do more than that then.
The is another scene where they find a secret tunnel in the heroine's house, and go to investigate, but they end up locked in the tunnel, with water rising because of the tide.
Of course, they end up getting married.

I read this book maybe 2 years ago. It was an ebook.

Thank you so very much in advance for your help (not knowing which book this was is driving me crazy!).

PS: excuse me for any grammatical error, I'm French and sometimes my English is not as good as I would like it.

[Melissa]

It could be a couple of books from The Bastion Club by Stephanie Laurens. Possibly either Captain Jack's Woman or A Lady of His Own. Both of these feature investigation of a smuggling ring, but I don't remember anything about spending time in India. Just a guess!

[Aerulan]

Sounds like a good book I hope it gets found. I don't recognize it, but if you haven't done this already you could take a look through this listopia list
Romance in India (and/or) Indian Heroes and Heroines and see if any of them are the one you are looking for.

There's also this list that's a little less specific but might be worth checking out too.

Romance from Around the World

[Morgane]

Thank you very much for these suggestions, but unfortunately, they are not the book I'm looking for.
I've looked through the lists, but I haven't found it... The fact that the hero is part indian is not a big part of the story, just a detail. I only remember it because it is unusual.

I think the book might be the 1st of a series about spies, but I'm not 100% sure.

[TinaNoir]

Sounds like The First Sinners by Kate Pearce.

[Morgane]

Tina wrote: "Sounds like The First Sinners by Kate Pearce."

This is the book!