The visitor arrived in orbit high above the earth on a fine northern hemisphere summer day. It came quite unexpectedly, though astronomers retrospectively tracked its trajectory back weeks as it approached the solar system from high above the plain of the ecliptic. It was enormous, a huge cylinder with mass and volume greater than the combined total of everything that humans had built in the history of their civilization. What was it? Where did it come from? Why had it come? Humans made every imaginable effort to communicate with their alien visitor, but it remained utterly silent. Then, some weeks after its arrival, it began to disgorge suborbiters. Brilliant, glittering, golden spheres, like giant, esoteric soap bubbles, began to descend on the peoples of the earth. Welcomed with tentative goodwill at first, the goldies soon resolved into the most enigmatic challenge humans had ever faced.