Young Irwyn Tremayne is petrified at the thought of following the family tradition of working underground in the Cornish copper mines. He blames himself for the death of his brother and is afraid to share the dark secrets he learns about body snatchers. Irwyn's widowed and depressed father needs a new start and books a passage for Irwyn and himself to Virgin Gorda to work in the copper mine there. Irwyn considers running away but wants to keep his promise made on his mother's deathbed to take care of his father. The rough sailing passage across the Atlantic presents no end of adventure and trouble. Will Irwyn find his true courage at sea?