Later she began working as an intelligence agent for the Soviet Union, travelling secretly to Moscow just as some of her comrades were being executed in Joseph Stalin's Great Purge, after which she resigned from the party.

This is widely assumed to have led to her unexplained disappearance in New York City in June 1937 as the likely victim of an assassination squad, possibly because she had been associating with Trotskyists.

[2] From 1907 to 1909, Poyntz was "Special Agent for the U.S. Immigration Commission," working in Chicago, Milwaukee, Philadelphia, Utica (New York), Lawrence (Massachusetts), and other cities.

She taught at Barnard College for the 1909–1910 academic year, when she was an assistant to history professor James T. Shotwell, who was well known for his liberal and pacifist views.

She was instrumental in labor-Left reform organizations such as the U.S. Immigration Commission, the American Association for Labor Legislation, and the Rand School of Social Science.

In 1936, Poyntz secretly travelled to Moscow to receive further instructions from Soviet authorities, and was seen there in the company of George Mink (alias Minkoff), an American later implicated in the disappearance of several Trotkskyists during the Spanish Civil War.

[3] Poyntz disappeared after leaving the American Woman's Association Clubhouse at 353 West 57th Street in Manhattan, New York City[9] on the evening of June 3, 1937.

[10] A police investigation turned up no clues to her fate, and her belongings, all of her clothing, and hand luggage in her room appeared to be untouched which suggested that she had not intended to leave the building for very long.

[11] In early 1938, Carlo Tresca, a leading Italian-American anarchist, publicly accused the Soviets of kidnapping Poyntz in order to prevent her defection.

Elizabeth Bentley stated she was told by Jacob Golos in the late 1930s, and later by KGB officer Anatoli Gromov in 1945, that Poyntz had been a traitor and was now dead.

Author Benjamin Gitlow wrote that Poyntz was disillusioned by Stalin's purges and was unwilling to continue as an espionage agent for the USSR.

In August 1936, the NKVD arrested Putna and accused him of maintaining contacts with Leon Trotsky, from whom he had allegedly received "terrorist directives."