The Arrival — Fred Saberhagen

Jonathan Doors
He is the head of the world's largest corporation, Doors International. A man of wealth and power, with the resources to reshape the world. A man whose life is about to change forever....

In the early days of the twenty-first century, the Earth stands still to hear the message:
"We are the Companions..."

The Taelons have arrived from beyond the stars on a mission of mercy, to help humanity claim its destiny. Contacted by these Companions, Jonathan Doors helps introduce the aliens and their fantastic technology to the world. But there is a dark shadow behind the Taelons' bright promises, and once it is revealed to Jonathan Doors he will become their greatest enemy....