UNTAMED - book 3 in the Without Mercy series.

Nelly Rosato grew up in a small fishing village where hard work and heartbreak were simple facts of life. Roger Jenkins was born to wealth and privilege. Until he met the wildcat from the north, his heart remained free.
Having lost her entire family by the time she was fourteen, Nelly knows how to survive. She has an enviable range of skills, including ancient navigation secrets learned from her Samoan grandmother.
The year is 1924 and the prohibition laws in the USA have opened an opportunity for Nelly and Roger. They build a business together: Roger supplies the liquor and Nelly delivers it. He risks his money. She risks her freedom and safety.
When her adoptive mother Mercy is senselessly murdered, it is one loss too many. Nelly wants revenge. Roger insists she wait for the local authorities to act.
While the police are chasing the wrong suspect, Nelly learns who killed Mercy. Ignoring Roger’s order that she stay home, she prepares for her most perilous run of all.
Untamed is the third and final book in the Without Mercy series. Your enjoyment of it will be enhanced by reading Unbowed, the prequel, first (available for free at most retailers). Each book contains an HEA for the main couple, but the murderer isn’t revealed until this book. The investigation begins in Unseen, continues in Unchosen, and concludes in Untamed. This book contains sexual and erotic scenes including power exchanges. If such content is likely to offend you, please don't read this book.