For twenty-three years a dozen space-alien refugees from have been hiding out on Earth, living inside various human hosts. When they arrived they hid their spaceship in the mud at the bottom of Lake Ontario, and when the "come home" call finally came, they happily prepared to get their spaceship and go home.
However, about that time someone spots a very strange sonar image in Lake Ontario, on the Canadian side. Both American and Canadian intelligence agencies send someone to check it out. At the same time, a member of Alien Hunters International is closing in on a couple of the aliens.
The story opens in mid-September on an overcast day with a cool wind and the occasional shower.
Four days before Button Day (The day that the aliens press the button that starts the re-activation of Professor Nothing, their spaceship)