But if she was a gray figure at the agency, Ms. Vertefeuille was also a tenacious and effective one, and in October 1986 was asked to lead a task force to investigate the disappearance of Russians whom the C.I.A. had hired to spy against their own country.
Almost eight years later, the investigation led to the unmasking of a C.I.A. employee, Aldrich Ames, as one of the most notorious traitors in American history. He had sold out the Russian agents — at least eight were executed — for millions in cash. His downfall was in no small part owed to Ms. Vertefeuille (pronounced VER-teh-fay), who brought to the mission a deep knowledge of Soviet spycraft and of her own agency’s workings. 
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