However, the books aren't the main attraction.
"Sometimes someone has read one or two of them, but it's more about the socialising. We are all working mums and if we don't make time to do this then we don't see each other," Sonia says.
There's never a shortage of conversation, as one book clubbers explains.
"I never feel there is much I can't say here; we talk about houses, children, problems, food, money... ".
The women say that no matter how bad they feel during the day of book club, the decision to go is always worth it because they get so much support and fun from the evening, lifting spirits and relaxing the nerves. It is a diaried event that only a holiday or sickness can cancel.
The monthly club started many years ago when Emma wanted to reconnect with old girlfriends after a stint of work in the UK. Each member takes turns at hosting; putting on dinner and drinks.
When the women are asked if they ever talk about the books, the answer is a unified "No!". Then someone pipes up: "Well, Rachel read one... once."
Television presenter, wife and mother of twins, Sonia still finds time for five or more social things a week.
"That's because I know, for me, I need that as part of monitoring and maintaining my wellbeing," she says.
New Zealanders have lost the art of connecting, she says, describing our 22nd placing out of 23 in the recent Sovereign Wellbeing Index report as "pretty scary".
Sonia says the report reminds people from all walks of life that it is important to allow ourselves to stop the hurly burly and make a plan to socialise.