Satan is coming to the end of his reign, but instead of gracefully passing the job to one of his sons, instead decides to do another stint as Ruler of Darkness. This upsets his two older sons, who head to New York to create hell on earth. This upsets the cosmic balance, which leads to Satan starting to disintegrate. So it's up to his youngest son, who is half angel, to head to earth and bring the two errant sons back. Naturally this is not a simple task, leading to much hilarity.