Reinhard Heydrich - mastermind or pawn ?
While true circumstances of Tukhachevsky affair (and subsequent Great Purge in RKKA) remain unclear to this day, there are certain facts that point to involvement of Germans, in this case particularly Reinhard Heydrich and his Sicherheitsdienst des Reichsführers-SS (SD). Story could be told from two sides, German and Soviet:
In late 1936, Heydrich got certain evidence from the former Imperial general, now emigre, Nicolai Skoblin, pointing out to conspiracy among Soviet marshals and generals (led by Tukhachevsky) to oust Stalin. Skoblin was, according to various sources, German agent for several years. Heydrich pondered what to do. Being convinced National-Socialist, for him the conflict between Third Reich and USSR was inevitable sometime in the future. In fact, these two countries were already in a proxy war (and not so proxy, considering that they had volunteers on the ground and air) in Spain. Weakening USSR would be beneficial in this case, but which side to choose ? Tukhachevsky, with his noble roots, seemed like much more formidable opponent than "Jew" Stalin (Germans doubted the story about Georgian origins) . Therefore, by exposing the conspiracy against Stalin, Heydrich could weaken Red Army and strike a blow against USSR.
To accomplish this goal, Heydrich and his men took evidence from Skoblin, forged some more about supposed contacts of Tukhachevsky with Germans, and then again, acording to various sources, used German diplomats in Czechoslovakia (in February of 1937) to deliver this documents to Czechoslovaks. Certain German diplomat supposedly told Czechoslovaks that secret negotiations between Soviets and Germans were being halted because Germans expect new leadership in Moscow very soon. Story goes that alarmed with this President of Czechoslovakia, Edvard Beneš delivered these documents to Stalin in March of 1937. Stalin, already suspecting Tukhachevsky, started Great Purge and the rest is history.
From the German point of view, action succeeded spectacularly, and when Barbarossa started in 1941 leaderless Red Army was almost destroyed. Heydrich was killed in 1942, and this was his peak achievement as a spymaster.
However, story has another side. What Heydrich and Germans did not know at the time is the fact that aforementioned Skoblin was in fact Soviet double-agent as mentioned in various Russian sources. Possibly they did not know that fact until end of the war, because Skoblin disappeared in mysterious circumstances in Spain in 1938. Therefore, documents that Skoblin gave Heydrich were in fact carefully prepared by NKVD which was already planning to remove Tukhachevsky by orders of Stalin and his closest associates. By giving documents to Germans and then getting it back, these forgeries became more authentic. Therefore, in this spy game Germans were mere pawns, that accomplished goals of Stalin and NKVD.
In the end, as mentioned before, Tukhachevsky affair remains a mystery. Did Tukhachevsky really wanted to get rid of Stalin (as he confessed in his show trial) ? It is interesting that he did not confess even there to be a German spy, as accused. After the death of Stalin, he was posthumously rehabilitated under Khrushchev, and Stalin accused of catastrophically weakening Red Army which led to millions of deaths in WW2. This is a view held by majority of Russian historians on the topic today. There is a possibility that Tukhachevsky really wanted to save country from Stalin or that Stalin simply feared powerful Red Army marshals and generals. What is a real truth is currently unknown.