The Doctor whirled about at the sound of his name, both hearts seeming to freeze in his chest as the source registered. That voice. That oh so familiar voice. His eyes widened. It couldn't be. No. No, it couldn't be. Not her. Not now. If she remembered him, her mind would burn.
He pushed away from the wall as though that might give him some momentum and began to hurry back to the TARDIS as best he could. He had to make it inside and send her back into the Vortex before Donna reached him. He had to leave and hope that he would be quick enough that whatever memories had surfaced faded back beneath the defenses he'd engineered for her.
Had the Doctor been thinking clearly, he would have realized that Donna shouldn't have been in New York City, and that if she knew him well enough to chase after him, she clearly wasn't in any danger from the metacrisis, or if she had been, it would have been too late for running away to help.