Numbers Game

First printed in Ellery Queen's Mystery Magazine mid-December 1984.
A prominent East European rocket scientist had just been selected to receive a prestigious award to be handed out in DC. The Reds controlling his nation will only let he and his wife attend the ceremony under the strictest of scrutiny. He had been passing vital intel on his latest creation but was stymied at conveying the mileage of the rocket. It is expected he would use his wife to pass that data but how?