In The Invitation, Will and Eden are a couple marked by the tragedy. Years ago they lost their son, which led them to separate, because neither of them could overcome that, which is the hardest thing that can happen to a person.
The emotional shock was so great that Eden even disappeared one day without a trace. Will worried, but he knew there was nothing he could do, for the loss of a child affects even more a mother.
One fine day, after a while, Eden returns. It seems that he has recovered, since he has remarried, something that Will does not bother him, since he knows that the memories that bind him would not let her be happy if he returned with him.
What happens is that Will notices something strange. Eden has changed, but it is not a normal exchange rate, since Eden is scary now, as if there were a different person inside her.