This is an easy problem....

...but shows one of the issues I have.

White to move

At first, and subsequent glance, this seems to be about a checkmate on g8, so I wasted much time trying to prove it was the case.

However, its not about that at all.

Simply Nxe7 is the solution.

On Qxe7, Qxc8 and White is up material !

What I am lacking is the visualisation that the Knight move opens the diagonal to the Rook. 

As soon as that is revealed, attempts to mate disappear.