Mari Prothero worries when her father Daffyd goes out fishing on the sea during storms, because she's not a fool; just because he's always come home safely before, logically that doesn't mean he always will. But at the same time, she knows he always will, thanks to the Prothero luck. When she turns 18, her father finally tells her the price that Protheros for generations have paid for their luck--a price she is now expected to pay in her turn.
Mercedes Lackey's Elemental Masters series is always great fun, and this installment is no exception to that rule, though it does seem a little light weight, compared to some of the previous volumes. It's nice to check in with a couple of recurring characters from earlier in the series, but Mari's journey of discovery and learning is something we've seen before, and the threats she faces don't feel particularly threatening. The fairy tale theme that all these books have isn't very strong in this one, either; in some other books in the series it took me a while to recognize the underlying story, but I eventually got it, and usually felt kind of tickled to be in on the secret. For this one I had to resort to the internet to figure out exactly which tales were involved, and then squint a little to see how they fit.
This is all just nitpicking; I quite enjoyed the book, and finished it in a couple of days, which I hardly ever have the chance to do any more. But I don't think this one is going to stick with me the way some of Lackey's other work has done.