In June, disillusioned members of the Latvian Riflemen began appearing in anti-Bolshevik circles in Petrograd .... As Latvians were deemed the Praetorian Guard of the Bolsheviks and entrusted with the security of the Kremlin, Reilly believed their participation in the pending coup to be vital and arranged their meeting with Lockhart at the British mission in Moscow. At this stage, Reilly planned a coup against the Bolshevik government and drew up a list of Soviet military leaders ready to assume responsibilities on the fall of the Bolshevik government. While the coup was prepared, an Allied force landed on August 4, 1918, at Arkhangelsk, Russia, beginning a famous military expedition dubbed Operation Archangel. Its objective was to prevent the German Empire from obtaining Allied military supplies stored in the region. In retaliation for this incursion, the Bolsheviks raided the British diplomatic mission on August 5, disrupting a meeting Reilly had arranged between the anti-Bolshevik Latvians, UDFF officials, and Lockhart (Cook 2004).

On August 17, Reilly conducted meetings between Latvian regimental leaders and liaisoned with Captain George Hill, another British agent operating in Russia. They agreed the coup would occur the first week of September during a meeting of the Council of People's Commissars and the Moscow Soviet at the Bolshoi Theatre. However, on the eve of the coup, unexpected events thwarted the operation (Cook 2004).

http://en.wikipedia.org/wiki/Sidney_Reilly