For a year, Tanny, a thirteen-year-old Japanese-American girl, will be living on the border of a Montana Indian reservation. Close to her new home is an old mission, which had once been part of an Indian boarding school. The school and dormitories burned in 1905, leaving only the church and graveyard behind.

The adjustment to Tanny's new school in nearby Sage Point is difficult until she becomes friends with Carrie Fox Paw, an Assiniboine girl who rides the school bus.

One night, the girls are drawn to a strange light below the mission's hill. Through the eerie portal of light, they are transported back to 1905 and become students at the old boarding school. They can tell no one where they are from and can find no way to escape their fate until the girls in Tanny and Carrie's ward tell ghost stories and hear that the father of one of the students, George Kicking Bull, has seen such a door. Now the girls know that the door has appeared before. They hope it will return.

With the irreverent Clara, who had turned from an enemy to a friend, the girls run away from the school and travel with George Kicking Bull, a sullen Blackfoot boy, to his reservation. George's father and an old medicine man offer the girls hope, but they must hurry back before it's too late and the portal of light closes.

As the time draws near to the date of the tragic fire, they race back to the mission. In a surprise ending, they not only find their way back but find out about themselves and their connection to the past as well.