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 with her sister adamant, her mother unyielding and her father no help at all, there seems to be nothing left for Fliss to do except sit back and let the ceremonies commence. However, when Richard's maneating ex-girlfriend Kat enters the equation, life becomes a little more complicated. And the discovery that Kat's husband Alex is the most gorgeous man Fliss has ever seen creates a brain-teaser too puzzling for even the cleverest of scholars...