Harry knew that the Order of the Phoenix was an organization Dumbledore had founded to fight Voldemort and his Death Eaters. He also knew that his parents, his godfather, Lupin, and even Mr. Weasley were all members.
Harry wanted to join the Order of the Phoenix too, and told Sirius as much. Sirius, however, refused him firmly.
"Harry, I admit you can already be considered a competent wizard. But we all know how terrifying an enemy we're facing. Until you come of age, we don't want you getting involved."
Beside him, Lupin nodded in agreement. "Sirius, it's rare to see you acting so mature."
"Do I act that immature?" Sirius protested.
Lupin, however, nodded earnestly, indicating that yes, he did, and very immature at that.
The others at dinner also opposed letting Harry and the others join the Order of the Phoenix just yet.
"I think we still have enough people. At least, we don't need to involve the children yet," Mrs. Weasley said. Seemingly to praise Sirius for his "mature" behavior, she even gave him an extra chicken leg.
"Forget about it, Harry." Ron spread his hands. "I've been hoping to join all summer."
After dinner, Harry learned a few more things about the rather unreliable Mundungus Fletcher.
First, on the day Harry had run into trouble, the man had gone off to snap up a batch of cauldrons of dubious origin, supposedly making a tidy profit. But after Harry asked a little about the amount, he scoffed.
It was less than the tournament prize money.
Although Harry and Hogwarts had fallen out badly with the Ministry of Magic after the Triwizard Tournament, Fudge had still left behind the thousand Galleons in prize money.
Harry had kept that money in his pocket as spending money.
Yes, spending money.