In The Other Side of the Door, Maria is a woman who is shattered, because it has happened to him the worst thing that can happen to a mother, that is to lose her son. It has not been possible to dismiss him, which adds even more to the sadness.
So when he discovers a ritual that allows him to say goodbye to him, he becomes a little happier. He does the ritual and this is when his nightmare begins, because something fails. He has been able to say farewell to his deceased son, but he has not closed the door to the other world.
That makes the door open and that his deceased son can come to our world, something that does, but not in a kind, but in a very aggressive way, so much that the one that has been his family is in danger.
Now, Maria has to figure out how to close the door, because if she does not get it, her deceased son is going to kill the whole family in a very cruel way.