FearfulSymmetry: Thanks, I look forward to hearing it. And sorry about the late reply, somehow the notification wasn't showing up for me.
No worries. GOG's notification system is dodgy at best.
Finished it last night. It's a relatively short read, but well done. The author splits it into three narrative lines: the expedtion in 1959, the investigation in 1959 and later, and his own research and expedition in the present, and alternates back and forth between them. It may sound like that would be confusing and chaotic, but he pulls it off very well. I felt it was easy to follow.
After laying out the facts and the theories, he then goes through each of the proposed theories/possibilities and eliminates them all, leaving, once again, a mystery. But he delves into another possibility. At the end, the author narrates the expedition timeline (in a kind of third person diary fashion) up to and including the day/night of the disappearance with what he feels really happened. For what it's worth, I think he's right.
A book you can read through in a night or two, depending on how dedicated you are, and well worth the time, IMO.