I like that Idea that the Dark fiqure could be Mac's Mom.. I also believe in a fit of jealousy Fiona let the shades to get Mac. She is going to betray JB in the end & be eaten by the shades herself.
Did U lasses ever see Weathering Heights or read the book? Do U remember that this governess hears all these mysterious noises and screaming at night. The Laird/gentlemen who owned the estate was hiding a mad (mentally) woman in the tower. Could it be that JB didn't make the noises but maybe he has been caring for something or someone who is cursed or mad.
By the way my boyfriend is sure that it was not truly Alina's body, that she is still alive and will be used to control Mac in some way later.