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 a passenger 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.