Jeffremov used the aliases Pascal and Eric Jernstroem to disguise his identity in messages[2][3] He had been working for Soviet intelligence since 1936.

[5] In September, 1939 Jeffremov using the alias Eric Jernstroem, arrived in Brussels from Zürich via Budapest and Odessa, travelling as a Finnish student.

[6] Upon arrival, Jeffremov enrolled in the École Polytechnique to study chemistry, assuming the veneer of an ordinary student.

[6] During the late interwar period, he was likely employed in the collection of technical information relating to chemical and chemistry, heavy industry.

[7] With the outbreak of World War II, Jeffremov was retasked with organising variously disparate groups in the Low Countries, into an effective espionage network that could collect political, economic and military intelligence.

[15] Germaine Schneider was the most important of the two, working as a courier that involved extensive travel across Europe and was Henry Robinson's contact to Soviet agents in Great Britain.

[20] Gurevich himself had hid in the house of Nazarin Drailly, a member of the group, to evade the Abwehr, before leaving for Paris.

[22] Probably the most important aspect of Jeffremov's work was the continued transmission of the intelligence provided by Harro Schulze-Boysen, that was couriered from Germany.

[24] In June 1942, Trepper ordered Jeffremov to begin transmitting as six months had passed since the raid on Rue des Atrébates on 12 December 1941.

[25] This was a fatal mistake, however, as on 30 June 1942, the Funkabwehr identified a house at 12 Rue de Namur, Brussels as the location of a radio transmitter and arrested Wenzel.

Jeffremov was to be tortured but agreed to cooperate and gave up several important members of the espionage network in Belgium and the Netherlands.

[37] When Schneider was arrested, she managed to convince the Sonderkommando Rote Kapelle that she not involved in intelligence work and was released.

[38] When released, Schneider decided to contact Leopold Trepper, the technical director of a Soviet Red Army Intelligence in western Europe to inform him of the arrests.

Simexco was a cover company that was used by the Trepper network in Belgium to provide funding for operations and to disguise its activities.