It's 1857 and 14 year old Joseph Armagh has arrived in New York Harbor with his dying mother and younger brother and sister, Sean and Mary. Just before his mother dies, he promises her that he will find their father and keep the family together. They stowaway in a cattle car and make their way to Philadelphia where Joseph discovers that his father has died and they are orphans. He is forced to place Sean and Mary in a Catholic orphanage while he finds work in a coal mine. He meets the beautiful and kind Katherine Hennessey, who loans him books so that he can educate himself. On the train to Titusville to find work in the oil fields, he saves the life of a stranger, Harry Zeiff and meets millionaire Ed healey who becomes his mentor.
To earn the highest wages possible, Joseph drives the "death wagons" at the mine. After a close call with the explosion of a wagon carrying nitroglycerin, Joseph goes into business with Ed at Healey Oil. He begins to quietly buy oil land options with Harry Zieff acting as his agent under his own company name, Xavier Oil. Living in Ed's mansion, Joseph begins a love affair with Ed's housekeeper Martinique. He convinces Ed to invest in the refinery business and Ed involves him in a gun-running scheme that ends badly. Joseph meets Ed's daughter, Elizabeth and is warned that she is off limits for any type of relationship. Joseph gives his promise that he will not get involved with her and he keeps it. Harry has fallen in love with Ed's mistress Emmy and an incident at the house when he is caught with her in Joseph's room, results in the death of Ed's bodyguard.
When Elizabeth Healey fails in her attempts to seduce Joseph, she decides to seduce the next attractive man she meets - Tom Hennessey. Tom becomes a senator and Elizabeth tells him she is pregnant with his child. She proposes a plan where Tom will use his political influence to create a false marriage record for her and a friend, Everett Wickersham who has been killed in the war. At a family dinner Ed shares the news of Elizabeth's marriage, the unfortunate death of Everett Wickersham, and the expected baby. He drinks to excess, collapses and dies. Ed's will is extremely generous to everyone - Emmy and Martinique are now both rich women. Martinique announces that she will go to Europe and Emmy marries Harry. Joseph receives 75% of Ed's estate and Elizabeth receives 25% with instructions that Joseph will invest her money for her. Joseph has built his own mansion in Green Hills and proposes to Elizabeth, but she says it's too late. Sean and Mary move into Joseph's new home, but Mary expresses her desire to become a nun and Sean becomes a union organizer. On her deathbed, Katherine Hennessey asks Joseph to marry her daughter, Bernadette and he agrees.
Joseph quarrels with Sean over the labor union issue and with Mary over her desire to leave and enter a nunnery. He rages about their lack of gratitude for all the sacrifices he has made in his life to provide for them. He says that Sean can go to Hell and Mary can go to Jesus and severs all ties with both of them. Alone in his big house, he now wants a family of his own and proposes marriage to Bernadette Hennessey. She understands that he does not love her, but hopes that will change once they have children. Sean organizes a strike against Joseph's company and when the militia are called in to intervene, violence erupts and many of the strikers are killed. Years pass and Joseph and Bernadette now have 4 children, Rory, Kevin, Anne-Marie, and Brian. Elizabeth Healey has married Tom Hennessey and Joseph vows to destroy him. Joseph uses his money and influence to expose Tom's involvement in a corruption scandal and he is politically ruined. Sean is falsely accused of an attack on the railroad and is sentenced to hang when he is wrongly convicted. Behind the scenes, Joseph intervenes to prove Sean's innocence - to protect the family name. He begins telling others of his plan to make his son Rory the first Irish Catholic President.
Tom Hennessey dies and Joseph goes to Elizabeth Hennessey and declares his love for her, undiminished by the many years they have been apart. She reveals that Tom was the father of her son. They agree that for the sake of his presidential aspirations for his son, he will not divorce Bernadette. Joseph attempts to bribe Senator Bassett to withdraw his support of the Alien Contract Labor Act. When this fails, he resorts to blackmail. To preserve his honor and keep his family secret, Senator Bassett withdraws his support the only way he can see - by committing suicide. His letter to Joseph tells him that with his dying breath, he has cursed Joseph and all his family. Bernadette hires a private detective who gives her proof that Joseph is having an affair with Elizabeth. She then gives him an assignment to find proof of her suspicion that Elizabeth's son, Courtney Wickersham is actually Tom Hennessey's son. Bernadette confronts Elizabeth with the proof in an attempt to blackmail her into ending the affair with Joseph. This plan backfires when Elizabeth freely admits the truth and now that Tom is dead, she no longer cares if the secret is revealed. Joseph tries match-making with his son Rory and Claudia Desmond, the daughter of a business associate. Rory is smitten with Marjorie Chisholm and asks Courtney Wickersham to introduce them. She has a boyfriend and offers Rory no encouragement. When he continues to pursue her and because he is an Irish Catholic, Rory is severly beaten by her boyfriend and his Harvard classmates.
Undeterred by the beating, Rory is relentless in his pursuit of Marjorie and she eventually falls in love with him. Both of their fathers are strongly opposed to the romance. Judge Chisholm doesn't want Marjorie to marry into an Irish Catholic family, and Joseph insists that Rory must marry an Irish Catholic girl for political reasons. Rory and Marjorie elope and are married by a Justice of the Peace. Courtney Wickersham and Anne-Marie Armagh are in love and they want to marry. Joseph has to tell Courtney that he is related by blood to Anne-Marie - Tom Hennessey was his biological father and Anne-Marie's grandfather. When they search for Anne-Marie to tell her, they are told that she rode off in a frenzy soon after returning home. Her horse returns without her and when they find her, she has suffered multiple injuries and is in a coma. Bernadette denies having told Anne-Marie that Courtney is a blood relative. Joseph and Elizabeth both feel intense guilt over the secret they kept and the consequences - they never see each other again. Rory and Marjorie are secretly and happily living together in New York when Joseph summons Rory to join him in London.
Joseph takes Rory to meet his rich and powerful friends who intend to "build their own president". Joseph insists that Rory must marry Claudia Desmond with an incentive of 20 million dollars or be disowned with no inheritance. Despite his intention to do so, Rory doesn't have the courage to tell his father about his marriage to Marjorie. Joseph returns home from London after learning of Rory's marriage by a letter from the Justice of the Peace and in a rage confronts Harry Zieff about hiding this information from him. America declares war with Spain and young Kevin Armagh joins Teddy Roosevelt's Rough Riders and goes to Cuba to join in the fight. Joseph meets with Judge Chisholm to discuss a plan to end Rory and Marjorie's marriage. Joseph offers him 10 thousand dollars a month to take Marjorie to Europe for 2 years. He has paid bribes to the Justice of the Peace and the court clerk to remove all evidence of the marriage from the official records. He has also prepared two forged letters to be delivered to Rory and Marjorie, each ending it with the other for personal reasons. When it is discovered that Kevin has gone to Cuba, Rory travels to Cuba as a "war correspondent" to find him and bring him home. When Rory finally finds Kevin, he has been injured in a sniper attack and he dies in Rory's arms.
When Joseph offers Bernadette a drink before telling her of Kevin's death, she becomes paranoid and thinking that he is trying to poison her, she is apologetic and confesses she told Anne-Marie that she was related to Courtney by blood, but she couldn't have known that it would cause Anne-Marie's accident. After she is told about Kevin, she becomes hysterical and tries to throw herself out of a window. Subdued by Joseph, she says they are all cursed. Bernadette, an alcoholic with severe emotional problems and Anne-Marie, still in a coma, are both sent into care at Woodville. It's 1912 and Rory Armagh is now a senator, married to Claudia Desmond with four children and plans are under way for his presidential bid. Joseph's youngest son, Brian has his own financial empire as owner of Xavier Aircraft and Xavier Films. After Joseph suffers a heart attack, he asks Brian to step in as Rory's campaign manager. Rory and Brian go on a coast to coast campaign tour and begin winning multiple primary elections. Winning the Democratic nomination is almost certain for him. Rory receives a telephone call from Marjorie and he races to her for a passionate reunion. On his deathbed, her father confessed the plan to separate them and she explains it all to Rory. They are just happy that they have found each other again. Elizabeth dies soon after a visit from Harry, where he discovers that she still loves Joseph. Harry tells Joseph that he wants to retire and travel now that he is 70 and his Emmy is gone. Rory takes the lead in the race for the Democratic nomination. The powerful financial organization that is backing Rory's bid for the Presidency summons Joseph to a meeting and asks him to have Rory endorse Woodrow Wilson for the Democratic nomination and settle for the Vice Presidential slot on the ticket. Joseph refuses, fearing that he won't live to see Rory elected president. Joseph telephones Rory to tell him that he no longer has the support of his powe