By 1944, the Axis were definitely losing the war on all fronts, and defeat was essentially inevitable. The Soviet Union, following their victory over the Germans at Kursk in 1943, launched a series of massive offensives across the entire Eastern frontline, and completely obliterated the German Army Group Center, robbing the Nazis of nearly a million men in an offensive called Operation Bagration. This was actually the worst defeat ever inflicted on Germany in history, even though it received far less attention than the Soviet victories at Moscow, Stalingrad, and Kursk.
In any case, the Germans aimed to make the Soviet advance across Eastern Europe as difficult as possible. The German High Command recognized that a military victory against the Soviet Union was impossible. That being said, the Soviet Union still possessed finite resources and were losing many more men and vehicles in battle than the Germans were. It was hoped that by inflicting as severe of losses as possible on the Soviets, the Soviet Union would agree to a truce.
Unfortunately for the Germans, this never happened and the Soviets continued to stampede across eastern Europe despite encountering mass casualties. Desperate, Hitler authorized Operation Zeppelin, a plan in late 1944 to assassinate Stalin and throw the Soviet government into chaos.
The Germans trained two Soviet defectors for the mission, who were both equipped with assassination weapons and given false documentation to help them slip through the Soviet lines and make their way to Moscow. The agents, who were one man and one woman, got married to one another and then were inserted via cargo plane into the Soviet Union. The agents then commandeered a motorcycle and drove onwards to Moscow, escaping the wreckage of the plane because it had been shot down by Soviet anti-aircraft fire.
They would have made it to the Soviet capital, and perhaps even been successful, had it not been for the fact that the Soviet military was tracking them throughout the countryside. Eventually, the spy couple was arrested at a checkpoint because they were suspiciously dry when it was pouring rain outside. The two were captured and executed seven years after the war in 1952.