Novel with a spy/assassin who helps the grand-daughter of a Nazi hunter, speaks Basque from learning it from a book, escapes a cave through water

I’m pretty sure I read this just a few years ago, but that it is an older story, maybe from the 60s or the 70s. I think it starts with the main character descending into a cave with someone else helping in running the belaying cable (which is a metal cable on an electric winch, I think) and then it either transitions to the airport attack or the origin of the main character. The former involves a set of terrorists opening fire on a group of Jewish Nazi hunters, only to be gunned down by a heroic CIA agent. The origin of the main character is a bit ambiguous in my head. He is a foreigner in the land where he is (maybe Japan?) and works his way up through the military hierarchy through his intelligence and hard work. Something happens that results in him being thrown into jail, and it’s there where he hones his skills through solitary practice, including learning various languages through the books in his cell. The latter results in an odd quirk where he speaks Basque Spanish in an idiomatic way because he learned entirely by puzzling out translations based on one or two books, so he gets a pronunciation rule wrong.

The second part of the book has the sole survivor of the airport massacre, the grand-daughter of one of those killed, seeking out the protagonist’s help. I believe she survived because the terrorists didn’t realize she was a part of the group. I think there was also something involving the customs agent being very distracted by the cleavage in her open shirt. Anyhow, her grand-father had done a service for the protagonist, and had told her to seek him out if she was in trouble, which she does. I vaguely remember there being a few legs to the trip, and her stopping at an inn on the way to where he lives and there being some confusion over money. Anyhow, she arrives, and learns that he’s mostly retired, living life as an aesthete, but he tells her he will help her. Not long after that, she gets up early to gather flowers on the nearby mountainside and she’s gunned down, leading to the main character setting off on a course of revenge.

The last part gets a little hazy. I remember that the bad guys freeze his assets, and try to bribe him into turning back by offering to unfreeze them. At some point, we wind up back in the cave, where the winch gets sabotaged and he winds up badly injured in the depths of the cave, only to escape through swimming blind through a hole in the cave that eventually opens up into a larger body of water (I was reminded of this book when reading Seizure in the Virals series, which involves a similar escape), and eventually has him getting his revenge on the person behind it all, who turns out to have been the CIA agent in the airport massacre, who was just killing the remaining witnesses.

I want to say that the title of the book was a foreign word. Shibari is coming to mind, but searches on that… well, it’s an erotic rope-binding technique, and does not seem to relate to the book I am looking for. I think I listened to it as an audiobook, and it was a usual novel length.