As part of what they conceived as a broader action against a collection of anti-fascist resistance groups in Germany and occupied Europe identified by the Abwehr as the Red Orchestra, in September 1942 the Gestapo arrested Terwiel along with her fiancée Helmut Himpel.

She completed her Abitur at a Gymnasium in Stettin in 1931, where her father, Johannes Terwiel, a devoutly Catholic Prussian civil servant, worked as a provincial deputy commissioner, while her mother was Jewish, which would limit Mimi's professional aspirations after 1933.

insbesondere die Pfandklausel (The General Terms and Conditions of Banks, in Particular the Deposit Clause), was ready to be submitted to the Faculty of Law and Political Science at the Albert Ludwig University in Freiburg in 1935.

A patient of Himpel's, the Communist writer John Graudenz, in 1939/40 brought them into contact with a broader resistance group in the city centred around the couples Adam and Greta Kuckhoff, Harro and Libertas Schulze-Boysen and Arvid and Mildred Harnack.

[7] For the Abwehr and Gestapo this, in turn, placed the couple in the frame of a wider European espionage network which, focusing upon Soviet contacts and Communist participants, they identified under the cryptonym Rote Kapelle (the Red Orchestra).

[8] On her typewriter, Terwiel copied anti-Nazi material supplied by the group that she, together with Himpel, Graudenz, the pianist Helmut Roloff, and others posted to people in important positions, passed to foreign correspondents, and distributed across Berlin.

This included Bishop von Galen's sermon condemning the Aktion T4 euthanasia program[9] and a polemic entitled "Fear for Germany's future grips the people" (Die Sorge um Deutschlands Zukunft geht durch das Volk).

[11] In a campaign initiated by Graudenz, on 17 May 1942, Terwiel, Schulze-Boysen, and nineteen others travelled across five Berlin neighbourhoods to paste the stickers on posters for the Nazi propaganda exhibition The Soviet Paradise (Das Sowjet-Paradies).