After the death of her father Ofelia's mother Carmen decides to marry Vidal, and is now pregnant with his child. The second world war is on. Vidal is a ruthless captain of the Spanish army.

Desperate to have a son, and in his presence, Vidal summons Carmen to his base - located somewhere in the rural hinterlands. The long arduous journey took its toll, and Carmen is now not keeping well. 

Ofelia spends time lost in her books, until she is approached by a fairy. The fairy takes her to an old faun. The faun tells her that she is an immortal princess, but she must successfully fulfil three extremely difficult tasks to prove that she is indeed of royal descent, otherwise she will remain, and die a human.

Will Ofelia succeed?