crux
noun
the decisive or most important point at issue
http://dictionary.reference.com/browse/crux
Quicksand page 19 PDF
“that was the crux of the whole matter. for Helga, it accounted for everything, her failure here in Naxos, her former loneliness in nashville.”
Helga realizes that she will not be able to solve he engagement issue. It is a problem that needs a resolution.
