Shopping for Fifth Year in Diagon Alley

Harry is wandering along Diagon Alley on his way to Flourish and Blotts for his fifth-year textbooks. He's spent most of the summer with Hermione, Ron and the rest of the Weasleys, and Sirius at the eerily elegant Black family townhouse, and is simply glad for a moment alone. Much as he loves his Wizarding friends, he's not really used to happy, functional families.

He's stopped outside Eeylops' Owl Emporium, thinking about getting some treats for Hedwig, when from a nearby alleyway he hears a voice whisper, "Imperio!"