Arc 1: The Room
The war had just ended, and the dark lord was finally defeated. The Aurors had killed or imprisoned his most dangerous followers, unlike in the previous war. Some families like the Malfoys had still managed to survive with a massively reduced fortune, but the pureblood ideology lived on.
It was not spoken of as openly as before, more in private conversations amongst some of the remaining purebloods, but it was truly the best that could be expected without wiping them all out.
Then something happened. It had started slowly at first, but it became more common for muggle-born witches to disappear without a trace. At first, people believed they were simply returning to the muggle world as the purebloods still held most of the wealth. Because the wizarding economy was still recovering from the war, there was already a shortage of jobs.
It was of course investigated, and people were questioned, but nothing ever turned up and with so few clues for the Aurors to investigate these cases eventually ended up archived and forgotten.