In the 1840's, when his followers are persecuted once again as a vigilante mob torches their meeting place and slays several of their members, Illiinois Mormon leader Joseph Smith urges his followers to take up arms and defend themselves. For his admonition, Smith is arrested on a charge of treason and found guilty, but before he can be sentenced, he is murdered in cold blood. Brigham Young reluctantly assumes leadership of the group and tired of violence, he decides to lead his followers out of Illinois after the army warns that they can no longer protect his people. This decision places Brigham in conflict with church member Angus Duncan, who urges the group to stay. The congregation, however, decides to follow Brigham, who leads them across an icy river to Iowa and across the great plains of the West. Joining them is outsider Zina Webb, who accepts the Kent family's offer of a home after the elder Kent is killed during one of the raids on the Mormons. On the road West, word comes of gold in California and, after Brigham falls ill, Duncan seizes leadership to lead the band to California. As they are traveling through the mountains of Utah, Brigham suddenly awakens in the hills above the great Salt Lake to announce that he has had a revelation and has learned that this is where they will settle. During the harsh winter, however, supplies run low and some of the women and children perish. Things look their darkest in the spring when a plague of crickets threatens the crop of wheat and Zina falls ill from starvation. Jonathan Kent has asked Zina to marry him, but as she lies stricken in her bed, his faith is tested. Brigham also has doubts, but just at the moment that he is about to renounce his leadership, a flock of seagulls appears from the skies to destroy the crickets and rekindle the faith of the Mormons.