Complex sentence: She entered the Ministry of Defence from Scotland Yard as a secretary in 1931; she worked for both MI5 and MI6 and became of one the security service's principal experts in Soviet Communism.
Split into simpler sentences: She entered the Ministry of Defence from Scotland Yard as a secretary in 1931 and worked for both MI5 and MI6. Bagot became of one the security service's principal experts in Soviet Communism.