The plot of Tron Legacy was:
The Creator comes down from his world to build another one. He makes a handful beings so that they may help manifest his will. One of these beings, the highest and most loved, which was made highest in the Creator's own image, acts as the Creator's right-hand-man and does his best to prepare the way for the will of the Creator.
As the Creator's will finds its destiny in a rise of flawed creatures, that first and most loved of the higher beings becomes enraged and rebels. Throughout his rebellion, he is distraught because all he ever really wanted was to show the Creator how good he was at manifesting the Creator's will. After all, he was the first and was supposed to be the most loved. Not these other imperfect lower creatures. This being brings evil to the flawed creatures and incites them against the Creator.
The Creator watches from afar, because he simply cannot be a part of the evil. There are still believers, there are still few remaining chosen ones. But they live in a world plagued by evil. The Creator's son, whose coming has been heralded, arrives on the scene, destined to re-unite the flawed creatures with the Creator. He walks among them as one of them.
Throughout the story, there is much treachery and deceit as loyalties are questioned and true destinies are revealed. Ultimately there is a final showdown between those loyal to the Creator and those who have been swayed against him. An artifact which contains the power of the Creator is the great weapon in this battle, a battle of light which takes place in the skies above the world made by the Creator.
The high being which betrayed the Creator, and which still seeks only the Creator's love above others, and which is forever torn between his compulsion-by-design to love the Creator and his own interpretation of the Creator's will, which he is forever compelled to manifest, is cast down. The Creator's son opens a doorway to the higher world. This is the world of the highest beings. And, through the work of the Creator and his son, this world will be opened to all of the lower creatures.