[1] In March 1939, Makarov became associated with Leopold Trepper, a Soviet intelligence agent who would later run a large espionage network in Europe.

[4] In 1937 he returned to the Soviet Union and 1938 began training as an intelligence officer[4] with a special additional instruction on the techniques of forging, achieving the rank of lieutenant.

[1] In March 1939, Makarov was ordered to travel to Belgium, via Stockholm, Copenhagen and Paris to meet and assist Leopold Trepper.

[1] Makarov initial purpose was to provide expertise in secret inks and forged documentation e.g. preparing Kennkartes for the group,[6] but Trepper's assistant Léon Grossvogel, had recruited Abraham Rajchmann, a known criminal, informer, a specialist in forging and the most unreliable of agents.

[9][10] In the summer of 1941, Belgian communist and Soviet Red Army Lieutenant Anton Danilov became an assistant radio operator to Makarov in a base the group had established in a house at 101 Rue des Atrebates in Brussels.

[9] Along with Danilov in the house was run by German Rita Arnould nee Bloch, who was courier and housewife along with Polish antifascist Zofia Poznańska, the cipher clerk.

[9] In another report, Makarov was sentenced to death by court-martial but his execution was stayed as he was the nephew of Vyacheslav Molotov.