<p>Fliss Blakeney is an English teacher in an all-girls school, but now she really wishes she'd paid more attention to her maths, and to her men. It takes her one year, eight months and six days to work out that if she marries Richard Trevelyn she'll make the biggest mistake of her life. What she didn't count on was her younger sister, Sally, agreeing to become Mrs Trevelyn instead. Fliss can hardly believe it. Surely he can't make her happy? But...