The story is set in Scotland and centres on plain-looking Maggie Wylie, whose wealthy family fears she will become a spinster. To ensure her marriage, her family strikes a deal with ambitious, young railroad porter John Shand: they will fund his university education if he agrees to marry Maggie in five years. John honours the agreement, but does not initially love her. Maggie quietly uses her intellect and wit to guide John's political career and write his speeches. Their marriage is threatened when John is tempted by the beautiful aristocrat Lady Sybil Tenterden.