The letter that the Reapers had sent to Sebastian was an invitation, telling him to go to a certain little town where they had temporarily rented a building. There, he would examine the corpses of the murdered nobles and tell the Reapers everything he could, particularly pertaining to the missing souls. Sebastian hadn't wanted to go, but Grell said that Will was paying for everything, including food and board, and the young Master demanded that he go to find out as much as he could for Phantomhive's purposes. So Sebastian packed a suitcase and then they all went to the train station to see him off—the young Master, the Undertaker, and Eleanora.
The Undertaker gave him instructions as they were heading for the train station: don't touch the Reaper's glasses; always be polite, especially to Will; don't make jokes about eating souls; try to act as less demonic as possible; don't touch the Reaper's glasses; will he remember not to touch the Reaper's glasses?
When he was done, the young Master took over and gave Sebastian some more instructions: find out everything he could about the murders; deduce if there's a correlation between the murdered people; try to find a pattern in the victims; etc; etc; etc; Sebastian was already bored and he hadn't even boarded the train yet.
They found the right train and then Sebastian turned to Eleanora to give her instructions regarding the manor: take care of things; look after the young Master; make sure the servants don't burn the house down while I'm gone.
"You'll only be gone for a week, you know," Ciel said as Sebastian continued rattling off rules.
"A lot can happen in a week, my Lord," Sebastian said, giving the young Master a look.
The train whistled; it was time to be off. Grell was already waiting for him in the car. Sebastian bowed to the young Master, shook hands with the Undertaker, and extended his hand towards Eleanora.
"Goodbye, Miss Black," he said softly. "Be careful."
Eleanora hesitantly extended her hand towards his, thought about her safety, and dropped her hand to her side, refusing to look at the butler.
Sebastian picked up his suitcase and boarded the train. It started to leave and he watched the three fade off into the distance—the young Master looking bored, the Undertaker waving, Eleanora not even looking at the train.
He sighed and settled back down into his seat. Grell took this chance to cozy up next to him.
"Sooo Bassy," he cooed, slinging his arm through Sebastian's, "here we are, all alone on a train, heading for the unknown…rather frightening, isn't it?"
"Lord save me," Sebastian thought and prepared himself for three hours of Grell-inspired agony.
The train left and Ciel turned to go home.
"Undertaker, are you coming back with us?"
"Oh, no; I have some business in town to take care of; you two kids go on without me," the Undertaker cackled. Ciel shrugged and began walking away, with Eleanora following behind him. "Wait, Miss Black!"
They turned back again; the Undertaker strode up and deposited a package into Eleanora's hands.
"Just something I bought for you," he winked. "I mean, now that you know and all. Who knows? You might find it useful. After all, it takes six months to plan a wedding." The Undertaker walked away, still giggling to himself like a madman.
"What is it? What did he give you?" Ciel asked, trying to look at it. Eleanora pulled the string and paper off it.
"It's a book."
"A book? What kind of book? What's it about?"
"Marriage to Demons: a human woman's guide." She frowned as she read the title and began flipping through the book. "It's all about demons."
"Oh, I have something like that," Ciel said. "Unholy books are great; they tell you everything you need to know; all you really have to do is ask."
So saying, they left the train station and stopped by in town to do some shopping. By the time they arrived back at Phantomhive, it was already rather late.
"I wonder how Sebastian's doing?"