The pictish child

In the book The pictish child twins Jennifer and Peter with their younger sister Molly have come from America to spend the summer with Gran and Da in Scotland. On a rainy day Jennifer and Peter and their little sister Molly go with Gran to visit three old friends at the Eventide Home. One of the old ladies gives Molly a talisman, a small stone carved with the picture of a bird on top of a snake. The talisman attracts both a time traveling young girl from the ancient tribe of the Picts and a dark magical force. The children work to return Ninia, the Pictish girl, to her own time; they must also protect themselves from the evil creeping mist. They also discover that one of the old women at Eventide is a descendant of the first owner of the talisman and will be able to take Ninia home. However, the children first had to rescue the women from their caretaker, who has them under a spell, before Mrs. MacAlpin can return Ninia to early Scotland.