They were the best of friends, they were the worst of friends ... Lizbet and Cassie are close, yet far apart. After a clueless upbringing (their parents' basic childrearing beliefs: 'play a trombone, see a monkey, get some fresh air'), the two sisters strike out in opposite directions, both desperate to escape...
Cassie is skinny, clever, charismatic, successful - every right-thinking girl's worst nightmare.
The one flaw in her quality-controlled life may be her marriage - and if there are any other flaws lurking, Cassie has them covered.
Lizbet is plumper, plainer, dreamier - more concerned about the design on her coffee cup than whether she can afford her new house.
She works reluctantly for Ladzmag, desperate to make her name as a writer, but stuck writing embarrassing articles on sex.
Her one achievement is her relationship with Tim, who thinks she's cute not stupid for asking why Jesus has a Mexican name.
Despite Cassie being the favoured child, she and Lizbet have managed to stay friends.
Perhaps because - as Cassie says - they've always wanted different things.
But that's about to change. Confronted by challenges that they never asked for, forced apart by mistakes not their own, will Cassie and Lizbet ever realise the real meaning of sisterhood, or will true nature ruin everything...?