Voldemort could hardly have been so bored as to come all this way just to listen to the Death Eaters report their utterly tedious experiences.
His purpose in doing this was simply to determine whether any of them were impostors who had taken Polyjuice Potion.
Although Polyjuice Potion could transform someone perfectly into another person, it had one limitation: whether one drank a sip or an entire cauldronful, the transformation could last no longer than two hours, after which they would revert to their original appearance.
To maintain it, they had to take another sip of the potion during that time.
Voldemort had exploited this limitation by gathering everyone together and watching them for more than three hours, only leaving once no one had changed.
This also showed just how badly Kyle had tormented Voldemort. He had even begun to suspect his own people.
Fortunately, Alastor Moody had prepared in advance, so his cover had not been blown.
After returning to Cornwall, he immediately entered a shabby shop selling Dark magic items, carefully shut the door, and approached a grimy mirror.
The hair of "Lainis" in the mirror had already begun to change, several conspicuous white strands appearing amid it, while his once well-fitting robes had become tight.
These were signs that the Polyjuice Potion was wearing off.
Moody took a bottle from the counter behind him, uncorked it, and gulped down a mouthful.
His hair returned to its dull golden color, and his robes fit properly again.
But when he opened his mouth, several gaps could clearly be seen in his teeth. Though they were in the back teeth and not easily noticed, they could still be spotted with close enough scrutiny.
Moody's throat worked, as though something had been forced up from his stomach, and he spat it