Complex sentence: He ended up at Dzhezkazgan, Kazakhstan, where he labored for several months until being called back to Moscow at the behest of the infamous General Ryumin, No.2 to Viktor Abakumov in the Soviet Union's State Security Department and engineer of the Doctors' Plot.
Split into simpler sentences: He ended up at Dzhezkazgan, Kazakhstan, where he labored for several months until being called back to Moscow. His recall was initiated by the infamous General Ryumin, No.2 to Viktor Abakumov in the Soviet Union's State Security Department and engineer of the Doctors' Plot.