Oooof, sorry but this was substantially the worst of the Arsene Lupin books so far (although I didn't read L'Eclat d'obus because all the reviews said that Lupin didn't appear in it and it didn't have the feel of a Lupin novel). And perhaps that's the problem. Leblanc has lost almost everything that made the earlier Lupin novels and stories so fun and enjoyable.
This book was nasty, brutish, ghoulish, callous, violent, but - even worse - stupid, mawkish, sentimental, colonialist, illogical, badly written and inconsistent.
Here we are thrown into the lives of people we don't know. We meet a saintly woman living in a convent after fleeing her psychopathic husband. We hear that her son and father were drowned escaping said husband. The husband is now dead, having been stabbed in an internment camp during WW1. But - as you might expect - things are not what they seem. In a news reel she sees a stone marker with her name on it, a number and an arrow. She travels to the spot, finds a body missing a hand, reports the body but when she returns the body has been moved. A trail leads her to The Island of 30 Coffins, or the Isle of Sarek. And from there the plot gets REALLY daft.
What follows involves massacres, awful gawkish sentimentality, an annoying disregard and glossing over of the lives and situation of anyone not directly involved in the plot, ridiculous coincidence, bad writing (although I admit much could be down to the translator), a submarine with a crew of "silent moors" (read: slaves), and a change in character of the bad guy from "evil genius" to incompetent uncontrolled buffoon in the blink of an eye.
Ach - honestly, it's just awful.
I honestly think that this book was so bad, that I'm now completely done with Arsene Lupin, after reading the whole series up until now. It's just lost a spark that made it fun and joyous and gained a dark unsatisfying heart.