Back to the Future Part III, Marty and Dr. Brown prepare to return to their own time after fixing the changes made by Biff in 1955, but their plans are interrupted when lightning strikes the time machine, causing it to disappear. Marty receives a letter from the past, written by the doctor, stating that he accidentally traveled to the year 1885 and that the time machine is buried and cannot be repaired under those circumstances. With the knowledge of the exact location where the time machine is buried, Marty travels back to 1955 to reunite with the doctor. Once they manage to restore the time machine using the technology available in 1955, Marty heads to the year 1885 to save the doctor and then return to their own time. However, they overlooked one crucial detail: while the future in 2015 had a solution for the time machine's power source with a recyclable reactor, such technology does not exist in the Wild West era. Now, Marty and the doctor have to find an alternate solution in order to make it back home.