In May 1940, Gurevich met Margarete (or Marguerite) "Greta" Barcza, the daughter of a Czech millionaire. During the invasion of Belgium when Brussels was being heavily bombed, Barcza met Gurevich while cowering in the cellars at 106 Avenue Émile de Beco in Brussels. In July 1940, when Trepper had to move to France to flee the German advance and start a new French network, he turned the Belgian network over to Gurevich. Gurevich, operating from a safehouse located at 101 Rue des Atrébates in Brussels, used Makarov as his wireless radio operator,
Zofia Poznańska as his cipher clerk,
Rita Arnould as a courier and housekeeper, and Isidor Springer, who worked as a courier between Gurevich and Trepper and as a recruiter. Gurevich reorganised the network and from that point only referred to Trepper on points of policy. In June 1941, Trepper sent
Anton Danilov to assist Makarov with radio transmissions. In September or October 1941, Trepper ordered
Abraham Rajchmann, a Polish career criminal and forger, to join Gurevich On 18 October 1941, among other assignments, Gurevich was ordered to contact the Harnack/Schulze-Boysen group to restore the connection between the Main Intelligence Directorate and the group. He was ordered to visit
Hans Coppi that was the groups' radio operator but was unable to repair the radio. On 13 December 1941, the Gestapo arrested Gurevich's WT operator Anton Danilov in an apartment at 101 rue des Attrebates,
Etterbeek in Brussels and Trepper happened to be in Brussels at the time, found out and warned Gurevich of the arrest. Gurevich's first concern was to arrange for Barcza to leave Belgium for France to ensure she was safe. Gurevich arranged travel documents with Rajchmann. At the same time, Gurevich was increasingly finding himself in arguments with Trepper. By that point, he was no longer part of the Soviet espionage network, was defeatist in his outlook and started to offer reasons why he was no longer using his transmitter. ==Arrest==