DISCLAIMER: No character/magicky thing belongs to me.
"—untraceable. I thank you, Sirius, but for the time being, kindly do not interfere. You must not forget that you are still a fugitive from the Ministry. Do nothing rash because it would be unwise. You would be straight back to Azkaban."
"I wouldn't want that," Sirius said.
"And, I warn you as everyone else in the Order has been, do not give Harry much information. It is best for the time that he is left without much knowledge. He must stay with his family for a time; he'd want to come too quickly and that would not be beneficial to the Order or himself."
"He has the right to know."
"Yes," Dumbledore agreed. "He does, but for a time that will be unwise. More and more owls have been intercepted and Lord Voldemort must not know that we have brought the Order back together. He must remain in the dark and that may mean, for the moment," he emphasized. "--that Harry must be as well. When he joins us at the end of the summer, he may know only what he needs to. I certainly agree with Molly," he sensed Sirius' budding protest and interrupted him. "He doesn't need to know just yet. On that note, I must leave. Kingsley and I have some business to attend to."
A loud pop indicated his departure. Alone, all he could hear was the scraping noise of the chandelier that Kreacher was dragging down the hallway. "—disgraceful, traitorous filth…" he hissed as he passed Sirius.
He sighed with exasperation at the old crank. This house would need a good degree of cleaning, the kind that Kreacher refused to do in the last ten years, a refusal caused the death of Mrs. Black. Sirius decided to revisit the old family tree, though he'd long since been scorched off of it. He'd run away to stay with James after… Well, he preferred just to remember the time he had spent with James' family. It was some of the best time he had ever had in his youth, outside of Hogwarts. "Alohomora," he murmured at the doorknob.
The door moved open when he pushed it, revealing a strip of light from the hallway onto lightless green walls. Countless scorch marks of traitors and squibs dotted the smirking faces of his unfortunate family—Bellatrix Lestrange, Narcissa Malfoy, their husbands, and Narcissa's son, his brother, cousins. Tiredly, he pushed the door to the point of being completely open to allow all of the light to flow into droughted room.
Stepping from the melting shadows, James Potter looked distressed and enraged all at once. "Sirius!" he gasped. "Harry is dead, Sirius; YOU LET HIM DOWN!" he roared. "YOU LET MY SON DOWN!" James' hand pounded into the wall to catch himself from falling as he doubled over, straightening himself again. "Why didn't you protect him? Why didn't you save him?"
Sirius realized he hadn't been breathing, about to respond to his friend, his very best friend. Something had occurred to him. This couldn't be James, the logical part of him stated firmly. This could only be one thing; one thing that lurks with the soul purpose of causing hurt when least expect. Even the dementors of Azkaban did not catch one while they were unaware; their presence was one so potent that even Muggles sensed it. Their closeness would result in chills, in feelings of complete helplessness.
The main difference between the two beasts who stole happiness was choice regarding them.
Dementors could feed on one's happiness until their deaths unless they could find enough control themselves powerfully enough to produce a Patronus. Even those with little self control could vanquish a boggart, simply with control over their thoughts. If he couldn't manage his own thoughts, it would be ridiculous; he'd be worthy of Snape's snide comments if it got out that he couldn't do something so simple as to oust a boggart.
He thought of Snape, of his funniest memory. In school, James had, well… "RIDDIKULUS!"
Hanging upside before him, as if his ankles were held by Filch's manacles, was the persistently over-formal Professor Snape. He was 15 or so years younger and wearing his uniform, emerald and silver tie askew and robes over his head. Snivellus had no pants, the doing of James, revealing grayed underwear. His face was invisible, but unlike in his true memory, Snape was not begging for mercy, just struggling. That made it more comical, less pitiful.
The sight lifted Sirius in a nearly literal way, like poor Severus. Before his mind had even registered what his spell had caused, his lungs were convulsing and choking around the air. The noises of laughter echoed through the halls that had long since absorbed all sound within the thick layer of dust.
The resonating of the uproar only further flustered Kreacher, raising his complaints but went unheard still. The boggart was twitching and shrinking, the sounds making it implode, smolder. Sirius had hardly noticed, regaining his cheer for the first time since Azkaban, for the first time since he lost his best friend.