Back to the Future
In 1985, Doc Emmett Brown shows teenage Marty his new creation: a car which can travel through time. The heart of the time machine is  "the flux capacitor," invented by Dr. Brown. The time machine needs plutonium to provide the power for the flux capacitor. Marty uses the car to escape from Islamic terrorists and accidentally goes back to the year 1955. Marty seeks out and meets Dr. Brown in 1955. The time machine is out of plutonium, and there is no plutonium available for the time machine in 1955. By chance, Marty knows the time and place of a one-time natural event (lightning strike) that can provide the power to transport the time machine and Marty back to 1985.