The end of the Civil War and the transition to the New economic policy in the European part of Russia were very painful. In the North-West of Soviet Russia, this is clearly illustrated by the two most important “cases” - the Kronstadt Uprising and the conspiracy of Petrograd Military Organization investigated by the Extraordinary Commission of the region. Despite the desire of the Cheka’s directorate to reshape the policy of the state security agency in accordance with peacetime conditions, in practice, due to the aggravation of the anti-Bolshevik movement the chekists continued to resort to the extraordinary methods that had been employed during the Civil War. The article analyzes the relationship between the Cheka and the PetrogubCheka (the regional Cheka of Petrograd) and the participation of high ofcials of the Cheka in monitoring the investigation of these cases. It also deals with the history of the well-known agreement concluded between V.N. Tagantsev, head of the Petrograd Military Organization, and the special agent of the Cheka’s Secret Operational Division Ya.S. Agranov who was appointed to conduct the investigation. For the first time the author of the article analyzes in detail the text of this agreement and the testimony of V.N. Tagantsev and comes to the conclusion that V.N. Tagantsev’s reputation of a mere victim of the Cheka mystifcation among émigré journalists, inherited by the contemporary historiography, was ungrounded. The article emphasizes the ambiguous position of the anti-Bolshevik movement in Petrograd that maintained close contacts with the leaders of the White emigration and at the same time remained internally weak and poorly stafed. However, it does not deny the fabrication of cases to the advantage of the authorities. The memories of contemporaries of these events help demonstrate a public reaction to the actions of the Cheka in the indicated period and trace the possible “channels” of receiving information about the aforesaid secret agreement by the public. Ultimately, along with the expansion of jurisdiction and the application of extraordinary measures in other regions, the operations of Chekists in the North West in 1921 also contributed to abolishing the Cheka and establishing the GPU under the NKVD of the RSFSR.