CAIN's JAWBONE seems like the sort of puzzle researchers of the Dead Sea Scrolls, regularly have to deal with. And something interesting to get to grips with.
If you want to become fluent in stylized English of the 1930's, a good start is in reading the memoirs of officers who served in the First World War. For example, Adventures of a Motorcycle Despatch Rider during The First World War by Major William Henry Lowe Watson. The tone of the book makes The First World War sound like a jolly adventure and a bit of a laugh. Then migrate through the various Biggles books, and dare I mention, the Billy Bunter books and comic strips?
I've just looked up CAIN'S JAWBONE on Amazon, and read the description given. Jo, it's a good job you're in Canada, and you daughter is in England. Don't shoot her. The problem is solvable through logic and intelligent reading.
I'm still trying to solve plot inconsistences and missing bits in my NaNoWriMo 50K words. Now up to 61K words.