A couple of books are free or on sale in a romance/police procedural series that I really like. The series is the Lord and Lady Hetheridge mystery series and it features two police detectives at Scotland Yard. The hero is a titled lord, 60 yrs old and a lifelong bachelor, the heroine is in her 30's, brash, from a poor East End background who has worked her way up through smarts and determination. Once they are paired together to investigate a crime, he falls for her pretty quickly.
The 5th book has never been on sale before so I was pretty excited when it popped up.
The first 3 books are also in a box set that sometimes goes on sale for $0.99. The books currently on sale are:
Ice Blue - Book 1, Free (I think this is perma-free)
Blue Murder - Book 2, $1.49
Blue Blooded - book 5, $0.99