Basically, a man gets on a flight and the plane gets hit by a malfunctioning UFO. The aliens aboard the UFO decide that since it was their fault, that they would take any survivors from the impact and transport them to other planets with humans on them since they couldn't have possibly survived the fall after the impact and can't have their presence be known. The main character is placed on a planet whose technology is equivalent to circa 1700AD.

He is a chemist so he has some ideas on how to help the society immensely, but has to be careful not to be too ambitious as this is still a very superstitious society.

GREAT series.