Cullen is in California with the Central Pacific Railroad and has to deal with the new workers.

Cullen and Fong find themselves in peril as they transport a locomotive over the Sierra Nevada mountains. The Swede gains Phineas' trust.

Cullen contends with violence in Chinatown set off by disgruntled railroad workers. Meanwhile, the Swede manipulates Phineas in his plot against the Mormons.

Cullen solves a Chinese labor strike in the wake of violence. Meanwhile, Durant pulls Mickey deeper into Union Pacific business.

Unexpected violence erupts in Chinatown during the festival of Tin Hau Don; Cullen confronts the Swede; and Durant involves Maggie in his latest scheme.

Cullen and Mei travel through the dangerous California wilderness with a precious cargo. Eva nurses Louise back to health.

Cullen and Durant meet up in Salt Lake City to talk to President Grant about the future of the railroad. Swede carries out his plan against the Mormons.

The Swede's cuddleous rampage on the Hatch homestead results in a long overdue showdown with Cullen.

Cullen thinks about making some life-changing decisions in Utah. Truckee adapts to life without Cullen.

Cullen's nitroglycerin experiment ends up being an explosive backdrop for the railroad life in Truckee.

Durant's plot to ransom himself takes an unexpected turn when Campbell arrives in town with the Cavalry to coordinate a rescue operation.

Mickey ends up having blood on his hands after working with Durant. Campbell returns to town and complicates Louise's life.

The race to finish the railroad comes down to inches, forcing all parties to contemplate the end of the line, and what the future holds for them.

The golden spike, government hearings and unpredictable actions mean new beginnings and endings for the survivors.