Death by Water (Phryne Fisher, #15)

'Who are you?' asked the doctor. 'You are not the standard cruise passenger, I can tell you that.' 'Thank you,' said Phryne in a self-possessed manner. 'You are correct. I am a lot of things, some of which do not concern you, but mostly I am Phryne Fisher.'

The nice men at P&O are worried. A succession of jewellery thefts from first class passengers is hardly the best advertisement for their cruise liners, particularly when it is likely that it is a passenger who is doing the stealing.
Phryne Fisher, with her Lulu bob, green eyes, Cupid's bow lips and Chanel travelling suits, is exactly the sort of elegant sleuth to take on a ring of jewellery thieves aboard the high seas - or at least, aboard the SS Hinemoa on a luxury cruise to New Zealand. With the Maharani - the Great Queen of Sapphires - as the bait, Phryne rises magnificently to the challenge.
There are shipboard romances, champagne cocktails, erotic photographers, jealous husbands, mickey finns, blackmail and attempted murder, all before the thieves find out - as have countless love-smitten men before them - that where the glamorous and intelligent Phryne is involved, resistance is futile.