WWII. Hungarian-Jewish Saul Ausländer is a prisoner at Auschwitz. He, along with several other men, are housed in a different part of the camp, as they are all given the work of knowingly corralling the other prisoners into the gas chambers, the prisoners who believe they are taking a shower and given food before they start work.
Saul and these men's work also entails disinfecting the gas chamber after use, going through the personal possessions of the dead looking for any items of value, and disposing of the ashes after the bodies are burned. It is after one of those gassings that Saul sees the body of who he believes is his illegitimate son.
Out of circumstance, the Germans want to conduct an autopsy on the body. Without telling the Germans, Saul goes on a mission almost at any cost to prevent the autopsy from proceeding, and steal the body to give it a proper Jewish burial, which also means having a rabbi preside over the burial.
To accomplish his mission, he will need the assistance of many of his fellow prisoners, which means telling them what he is doing. It is then that Saul learns that some of the other worker prisoners are trying to smuggle information out to show the world of the atrocities of the camp, while smuggle in items that will help in an uprising against their captors.
Saul may have some issues in dealing with the other men who may see their own task as more important and incompatible with his. But another issue may throw a wrench into what they are all doing when they realize that their own usefulness to their captors may soon be coming to an end, meaning their own lives.