The Sons of the Vikings by Hjalmar Hjorth Boysen

Witch Martha lived in a small lonely cottage down by the river. Very few people ever went to see her in the day-time; but at night she often had visitors. Mothers who suspected that their children were changelings, whom the Trolds had put in the cradle, taking the human infants away; girls who wanted to "turn the hearts" of their lovers, and lovers who wanted to turn the hearts of the girls; peasants who had lost money or valuables and wanted help to trace the thief -- these and many others sought secret counsel with Witch-Martha, and rarely went away uncomforted. She was an old weather-beaten woman with a deeply wrinkled, smoky-brown face, and small shrewd black eyes. The floor in her cottage was strewn with sand and fresh juniper twigs; from the rafters under the ceiling hung bunches of strange herbs; and in the windows were flower-pots with blooming plants in them.

Martha was stooping at the hearth, blowing and puffing at the fire under her coffee-pot, when the Sons of the Vikings knocked at the door. Wolf-in-the-Temple was the man who took the lead; and when Witch-Martha opened the upper half of the door (she never opened both at the same time) she was not a little astonished to see the Captain's son, Frithjof Ronning, staring up at her with an anxious face.