She reckoned that they were playing some kind of game having to do with the workings of the air traffic control system. Though she had never studied such things in any detail, she knew in a vague way that radar had limited range and that the structure of the air traffic control system somehow reflected that fact; a country’s airspace was divided into separate zones, each managed from a different control center with its own radar system. Airplanes in flight were handed off from one control center to the next as they made their way across the country. At some point they had stopped being the responsibility of the air traffic controllers in Xiamen and entered into a zone controlled from Hong Kong. Or perhaps by flying out over the ocean they had entered into a no-man’s-land that was not monitored or controlled by any authority. At any rate, she guessed that they had, a few minutes ago, reached one of those edges or seams in the system. Pavel and Sergei had then bid farewell to the air traffic controllers in the zone that they were departing and had gone into the power dive before they showed up on the radar screen, and came to the attention, of any other controllers.