Secrets by Lynne Barrett-Lee

Sisters Megan and Ffion have never had secrets, so when Megan goes to flat-sit all she's expecting is a rest and a change. When a stranger called Jack phones, Megan wonders who he is. Ffion behaves like she's just seen a ghost, and refuses to say any more. So is Jack a ghost? Ffion's not telling and when she disappears too, and the mystery deepens. Megan begins to fear for the future. She's always been the one who's looked after her little sister. Is this going to be the one time she can't? From Amazon.uk

A short romance. Megan is flat-sitting for her sister and suddenly finds out that her thinking that her and her sister never had secrets for each other was a lie. Her sister has a major secret that she has kept for many years.
Okay but not very good. The mystery is all about how the sister cheated in her marriage and made her husband the scapegoat. Glad I didn't pay for it.

This book qualifies for:  
100 books in a year Reading Challenge 2012, 
Goodreads 2012 Reading Challenge, 
2012 Ebook Challenge,
A-Z  Book Challenge 2012,
Why Buy the Cow? Reading challenge 2012 ( this book was free on Amazon.uk the 23rd of August 2012)