A/N- The story of Fawkes and the story of Dumbledore are happening at about the same time, so don't get confused if their stories overlap and seem to be in the past.
Fawkes started his flight away from Hogwarts, carried by a strong tailwind. The bird flew over Hogsmeade, and landed in a small cave in the mountains near the village. He searched the cave, but the only sign that his recipient had ever been here was a small pile of ashes in the middle of the room. The ashes were cold, which told Fawkes that the man had left the night before. The phoenix searched the cave again, looking for any sign that would tell him where the man was now. As the sun began to set, a ray of light reflected on a small crevice in the back of the cave. Fawkes flew over to the crevice, and used his beak to pull out a tiny bit of parchment, with only one word.
Hollow.
Satisfied with the message, Fawkes flew off again.
Dumbledore watched Fawkes fly away, lost in thoughts of this new, mysterious man. When the phoenix was no longer in sight, Dumbledore crossed his study, and opened a cabinet on the other side. Inside was the Pensieve, the silver bowl almost overflowing with water. Dumbledore approached the shelf behind the Pensieve, labeled Godric's Hollow, Meeting Gellert Grindewald, 1899. Dumbledore carefully tipped the contents of the bottle in to the Pensieve, and swirled the mixture with his wand. He plunged his face into the bowl.
Dumbledore found himself on a dull winter day, watching himself bump into a young Grindelwald. Dumbledore's young self noticed the badge Grindelwald wore, which he had recognized to be the Deathly Hallows, and both boys knew they had found someone they could finally relate to.
The older Dumbledore wondered, Could Gellert be the man who is contacting me? But he dismissed the thought quickly. Grindelwald was stuck in Nurmegard, and couldn't care less about what happened in the outside world. Dumbledore pulled himself out of the memory.
Dumbledore exited his study, and instructed the gargoyles guarding it not to let anyone but himself in, even if they had the password. Dumbledore exited the castle, and made his way to Hogsmeade.
He passed the snow-covered shops that he usually stopped at on visits to Hogsmeade, and his gait and the look of consternation on his face told everyone who could see him that he was not to be disturbed.
Dumbledore entered the Hog's Head quietly. He approached the bar, and whispered to his brother, Aberforth, "Clear the bar. Now". The look on his brother's face told Aberforth not to argue."Everybody out! The bar is closed for the night!" Aberforth yelled.
As the people in the bar left, Aberforth locked the doors and brought his brother into the back room, where the picture of Ariana loomed over them. "What's going on?" Aberforth asked. "Trouble",Dumbledore replied, and told Aberforth the events of the day.
"So Fawkes knows where this man is, correct?"
"I presume so. Why?"
"I saw Fawkes fly overhead earlier today. He landed in the mountains."
"Thank you brother. Please send an owl if you find any other information." Dumbledore hastily left the bar.