A Matter of Sin by Jess Michaels

Lady Isabel Avenbury has one more sister to off into marital bliss and then she has decided to take a lover. Once she is no a "proper chaperone" for her single sister, she can find someone to fill her lonely nights. Hopeful to find an advantageous match for her sister, Isabel joins the house party at Marquis Lyndham's home. But what happens when Isabel finds herself attracted to the host that she thought might be a match for her sister?
Seth Rowland, Marquis Lyndham, is not looking forward to the house party his mother is throwing to find him a bride. He can't abide all the empty headed misses that are paraded in front of him.  But what happens when one of the chaperones catches his eye?
Seth and Isabel decide to have a brief affair during the house party but when you throw a copy of the Ladies Book of Pleasures into the mix everything changes. What adventures lie ahead for the two of them?
Every time I start a new series by Michaels, I immediately want the rest of the books in my hands! She sucks me into the friendship/relationships of these characters and I want to read all their stories!
This story starts with three friends (Isabel, Grace and Jacinda) talking about the new book that has hit the town, Ladies Book of Pleasures.  Made brazen by their discussion, Isabel (a widow) announces that she is ready to have an affair but not until she sees her youngest sister married. She doesn't want to hurt her sister's prospects on the marriage mart. But once this decision is made, she becomes smitten with the first male she encounters. She doesn't know what to do. Luckily her friend, Grace is also at the house party so of course they have a heart to heart. I love the relationship between Isabel and Grace (we don't see much of Jacinda). Everyone should have a bestie like that!!
Seth and Isabel together just sizzled!! It is interesting to learn that they had each been attracted to the other before Isabel's marriage, but because of Seth's youth (no way would he have married that young) nothing every came of it. That slow simmer really exploded off the page when it finally ignited! I just loved how the two of them interacted with each other. Isabel was a bit shy at times but learned how to be a bit more aggressive in the relationship when her confidence grew. They both had to figure out if they were going to do what was best for their family or best for themselves...
I sat down to just start the book and I ended up not being able to put it down. I finished it in one setting! 
I CAN NOT WAIT FOR THE NEXT BOOK IN THE SERIES!!

You can get this book at Amazon, Barnes & Noble, Kobo, Google Books and Samhain.