"Spell My Name with an S" is a science fiction short story by American writer Isaac Asimov.
A complicated series of events ensue in which Sebatinsky is investigated by the Security establishment, who feel that he must be trying to hide something.
His Polish origins lead them to suspect that he is trying to distract attention from relatives in the Eastern Bloc.
They discover that he does have a distant cousin who is also a physicist, which leads to the discovery that the Soviet Union is working on gamma ray-deflecting shielding as a nuclear defense.
The story concludes with the same two beings making another bet to put everything back the way it was with another minuscule alteration, with the likely consequence that the world will end in nuclear holocaust after all.