Moriarty borrowed Severus Snape's office fireplace and used Floo Powder to return to Diagon Alley. The only price was handing Severus Snape a batch of Mollifying Solution at the start of term.
Moriarty readily agreed. Cold on the outside but warm at heart, Severus Snape was really just assigning him homework.
After stepping out of a fireplace somewhere in Diagon Alley and onto the street, Moriarty saw his House-elf, Luke.
Luke had spent the past few days waiting in Diagon Alley for Moriarty's classmates. Whenever a student Moriarty had invited to visit the Castle arrived, Luke would take them to Slytherin Castle.
After asking around, Moriarty learned that William had been the first guest to head to the Castle. The upperclassman seemed determined to cut loose after graduation; according to him, he would travel around Europe after attending Moriarty's gathering.
Moriarty only hoped he would not run into any strange people and end up with something attached to the back of his head.
Penelope was also worth mentioning. The moment she returned to London, her parents took her away, so she could not attend the gathering.
Then there was Bill. This solitary, unconventional Weasley was as elusive as ever. He vanished immediately after graduating, and even Charlie did not know where he had gone.
After buying a large quantity of ice cream from Florean Fortescue's Ice Cream Parlor, Moriarty had Luke take him back to Slytherin Castle. Two days later, the gathering began as planned at dusk.
The Castle's Great Hall had been redecorated by Ingo and Luke. The enormous Lemurian Crystal chandelier gleamed with crystalline brilliance, while all manner of magnificent antiques, artworks, and reddish-brown furniture had been arranged neatly enough to dazzle the eye. The finest drinking sets lined the walls, making the Little Wizards restless with anticipation,