Elizabeth has her "8 month" baby (but doesn't fool Aunt Agatha or Demelza).
Dr Ennis gets married and goes to war. (but no honeymoon for him)... this is a slight change from the book.
Presumably the later episodes will have Ross rescuing him from his POW camp.
The episode is based on the book "Black Moon" which I am rereading at Scribd...
but someone has reecently reposted the audiobook on youtube, so you can listen to it (before the copyright cops find it) LINK link2