Augustus and Araquill were chatting, and then, Augustus brought up a question.
"What's that book again?"
Augustus said, talking to his best friend, Araquill, while heading to Flourish and Blotts, in the midst of Diagon Alley.
Araquill sighed. He hated explaining things to anyone.
They stopped in the middle of walking, and Araquill raised his head.
"Hard to explain. You'll see it. Well, not really..."
Araquill mumbled.
Augustus was confused. What was his best friend talking about? More importantly, what did he mean see?
They went inside the beautiful place, which had shelves and shelves of books, ready to be purchased.
Augustus obviously was ready to see what his best friend was talking up a storm about.
Augustus had 3 things on his list.

1. To figure out what this meant.
2. Let Araquill buy it.
3. Wander around Diagon Alley swooning over the stuff he couldn't afford.

Araquill already went to speak with the clerk, while Augustus simply lounged back, and noticed an odd book sitting on shelf 160. He had to see it.
He picked it up. It read, "Autobiography of a Journal". He flipped through it.
Turns out, he didn't need to write in it or anything. It was already filled in. The journal filled entries for itself.
He was so caught up in it when Araquill finally screamed.
"I've found it!"
The clerk was visibly annoyed, but he handed Araquill....air?
Augustus ran up to talk to the clerk.
"Sir, are you sure my friend isn't getting scammed?" Augustus wailed out in concern.
The clerk chuckled, and then brushed it. Dust was on the "cover".
Augustus's jaw dropped. What is going on?!
Araquill chuckled, and Augustus got the hint; its a INVISIBLE book!