I didn't realize until I finished reading this book by Nicola Moriarty that she is the sister of Liane Moriarty. I've read a number of Liane's Australian-set novels and liked them. The Fifth Letter is also set in Australia. Four women have been friends since middle school and they try to get together every year for a vacation together. They are now in their thirties and have gone to the beach (in the winter!) for a week. The organizer of the group, Joni, decides that they should all write an anonymous letter divulging a secret they've never shared with each other and then they'll read one letter aloud each night. This alone would make for quite a story but it also turns out that someone wrote a "fifth" letter. They wrote that letter first, then changed their mind about the secret they wanted to reveal and wrote a different letter to be shared. Of course Joni finds the fifth letter. Much drama ensues.
While I thought this was well-written, it took a while to get going and I didn't think the secret in the fifth letter was really all that "holy cow, I can't believe it!" Let's just say I was honestly glad to see someone getting psychiatric help at the end of the story. And I have to say that the epilogue, especially the very last line, was just too much. I think the author thought she was being clever but my reaction was just "ugh."