Carolina and James Baldwin's wedding had been the happiest day of their lives, but now family problems and the ever-increasing demands of the B&O railroad are combining to challenge the newlyweds' continued happiness. When James' father desperately needs their help, Carolina struggles to forgive her father-in-law for past wrongs, driving a deep emotional wedge between the young couple.
James is assigned to supervise the building of the distant Kingwood Tunnel, and he and Carolina decide to move their growing family from the comforts of their home in Baltimore to a small rural town in the Allegheny Mountains. No longer do they have to endure being separated, but soon the pitiful living conditions take their toll, and complications from both the severe weather and the escalating tensions among the Irish railroad workers conspire against them.
A young Irish worker, Kiernan O'Connor, befriends the Baldwins, despite the protests of his brother. Young Victoria, Carolina's stepdaughter, is enthralled with the gentle, handsome Kiernan, but will the upper-class Baldwins ever consider him a proper suitor for their daughter? And will their friendship prevent James from stopping Kiernan's brother from carrying out his destructive plans before it's too late?