Harry meets Luna Lovegood at the end of his second year when she comes to thank him for saving her only friend. They get to talking and Harry isn't immediately put off by her odd nature so she invites him to go on vacation with her. He accepts, not expecting much to come of it. Surprise surprise, Luna shows up at his house with her dad, they piss off the Dursley's. Luna's weird dad decides Harry would be much better off looking for odd creatures with them than trapped with magic hating muggles.
Weird things happen. A lot. Knowing Harry had slain a basilisk, the Lovegoods take him across the globe looking for another. Head Auror Delacour of the French Ministry of Magic learns of Lovegood's presence in France. His family hosts the Lovegoods, intent on asking Harry to help with a rumor of a basilisk den deep in the country. Delacour, who is wealthy and powerful, updates Harry on the status of the English "Mass Murderer" Sirius Black. He includes a thorough background report on everything he can find out about Black.
Harry's not used to the respect and recognition he's shown. Auror Delacour's veela sister decides it's her destiny to aid Harry's recognition of his own abilities and power. The Lovegoods leave him in the Delacour's capable hands for the rest of the summer. The Harry who arrives back at Hogwarts for third year is much different.