So the case of a 'hacked wallet' changed into the case of a disappearing wallet.  With jim618's recovery suggestions I have my bitcoin back.  

Basically created a new wallet and this time created it on an external disk - so, no hot wallet any longer.  The method to import private keys is a little fiddly, but eventually it worked fine and my wallet is now restored with all of my bitcoin.  

Now I can drink that beer!  

Backup!  Daily!  Don't be lazy like I was and just accept your wallet software.  Learn it .. play with it, so that you know it, where it puts stuff and what it calls things and so on.

Great Tech Support from Jim618 and thank-you all.