Liane Moriarty.

Liane Moriarty.

Liane Moriarty has no idea what secrets her husband Adam might be keeping from her.

''He's a very private person,'' she says. ''He's probably the one who has the secrets but I have no idea what they could be.''

She won't give up her biggest secret either - ''I've got really good friends in Canberra'' - but can't think of anything that she'd really need to keep hidden.

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''I'm not very good at keeping my own secrets, I'm quite open about that … I can't see the point in keeping a secret if it feels like it's just a secret for the sake of being a secret.''

Moriarty has been thinking about secrets, and how people choose to keep them, or tell them, during the writing of her latest book, The Husband's Secret.

In it the suburban lives of a collection of women are turned upside down by such decisions. A husband with a confession, an affair too close to home, an unsolved murder from the past that comes back to haunt them all.

The inspiration for the book came from an article Moriarty had read about real-life death-bed confessions. Christian Spurling confessed on his death bed to faking a notorious photo of the Loch Ness monster; another man who thought he was dying of cancer confessed to a 30-year-old murder, didn't die and went to jail; a songwriter who admitted to plagiarising a lullaby melody.

''The article, particularly the story of the man who didn't die, got me thinking,'' Moriarty says.

''I was intrigued by that overwhelming desire to share your darkest secret.''

In the book Cecilia discovers a letter from her husband John-Paul that says: ''For my wife, Cecilia Fitzpatrick. To be opened only in the event of my death.''

Would you open it if your husband wasn't dead?

''Adam says he knows if he would write a letter like that I would have opened it immediately.''

I'm with her. So, too, were many of her friends.

''I kept putting the premise to my female friends and asking 'Would you open it?' '' she says.

''I loved watching their faces as they struggled with the ethical dilemma. Their answers were varied but they all agreed they would certainly want to open it.''

Cecilia does open the letter and it's what happens afterwards that takes the story in an interesting direction. What would you do if the secret was so dark it could destroy your family? If you knew for sure that the man you were married to, had been married to for years, was no longer this man?

It's not only Cecilia who is dealing with a secret. Tess discovers that her husband, Will, is cheating on her with her cousin and best friend Felicity and ends up with a secret of her own. Rachel is dealing with the unsolved murder of her daughter, a crime that ties them all together.

Moriarty wonders why people do keep secrets.

''It's because of shame I think, that's what it's mainly about,'' she says. ''Why else do you keep a secret unless you're protecting someone else or it's shame over what you've done.

''I think the book is about that, there seems to be a theme about feeling ashamed.''

There is also a sense of feeling overwhelmed. All the main female characters, particularly Cecilia and Tess, middle-aged wives and mothers, are leading lives filled with too much detail. On the morning Cecilia finds the letter she's dealing with her daughters, the Berlin Wall, The Biggest Loser, Tupperware and perimenopause. ''Here I am, a typical suburban mum.''

Moriarty is 46, with two children, Anna, three, and George, five, who has just started school. The author is in the middle of the setting of her book, the suburbs, the schoolyard.

''I think this book would have been very different if I had have written it in my 20s,'' she says.

''Everything is so black and white when you're in your 20s.

''Then, when you get to my age, you've seen so many things happen to yourself and your friends and your family.

''People can forgive things that you thought were unforgivable.

''When you have children, too, that changes your perspective again.

''In your 40s everything seems quite grey.''

Which is what makes the decisions of the characters quite real, quite, to be honest, disturbingly true. What secrets could you keep if you knew your world would be turned upside down? What could you forgive? What could you forget?

There's an interesting epilogue to The Husband's Secret. Moriarty finishes it off this way:

''None of us will ever know all the possible courses our lives could have, and maybe should have, taken.

''It's probably just as well. Some secrets are meant to stay secret forever. Just ask Pandora.''

The Husband's Secret, by Liane Moriarty. (Macmillan, $32.99)