What is says on the tin.
If we follow the "classic" narrative of the Eastern Front and accept Stalingrad as the Third Reich's "high water mark", is there anyway (short of ABS/divine intervention) for the Nazi's to slow, or even halt (but not reverse) the Soviet advance? If so, how does this affect the Western front? If it looks like the Soviets are delayed or stalled, how do the WAllies react?