Cal gets more and more enamoured of this woman, while other, less savoury parties are trying to acquire the chart and to put Cal off getting too involved. But are they trying to get the "treasure" for themselves, or are they actually telling the truth, and is Cal letting himself be drawn in by a pretty face and a black heart?
It's all good stuff, and Pérez-Reverte has done his revision: all of his nautical banter and explanations sound damn authorative to me. There's a lot of navigational detail here, and there's a lot about a sailor's point of view. The tail is drawn out a little too far, but it's a convincing read. I'm sure that someone who reads faster than I do would enjoy it more.
I felt slightly disappointed by the ending, but that's down to expectations; it makes sense how it finishes, although it's not nice and tidy.
[1: At least, I think he was called Cal. I don't have the book to hand.]