The school day was finally over, and Gaius had even managed to turn over his one detention to the care of Argus Filch, much to the dismay of the Fourth Year Gryffindor who had transfigured his Slytherin rival's cat into a singularly ugly chamber pot. It had taken Gaius all of his study period to turn the poor feline back into its proper form, and he'd been so annoyed at both the loss of time and the bizarre quirks his own magic had developed lately that he'd given the perpetrator an entire week of detention. In his annoyance he'd even forgotten about the Fair that night until it was almost time to leave for the day. Fortunately Filch had been available, and so Gaius had remanded the wide-eyed boy into his care and taken himself off for home, eager to leave the cares of teaching and the concerns about all the magical mayhem at the school behind for one evening.
Slipping back into human form from his mad dash back from the school, he opened the door and stepped inside Haven's Loft, smiling as he immediately caught sight of Sirius, looking like sin incarnate as he glanced up expectantly at Gaius' arrival. He caught a movement out of the corner of his eye, but he wasn't too surprised to see Lily Potter there, probably waiting for Harry to return home. She never seemed to even notice Gaius' presence in the house and had never spoken to him, which he wasn't certain whether to ascribe to disapproval over his relationship to Sirius, his connection to Severus, or to some odd quirk of her own. For a ghost she was somehow oddly incomplete, for lack of a better term, but since he'd never known her in life it was difficult to judge whether the aloofness was intentional or because she simply didn't see him.
What was far more unusual was the presence of another ghost, one whom before now Gaius had never seen, even though he had heard both Harry and Sirius discussing his presence. Apparently the spirit of James Potter did notice Gaius, and had taken great pains to never allow himself to be seen if Gaius was around. That behavior did seem like a deliberate snub, but Gaius was long past it bothering him - Severus had waxed quite eloquent on the subject of Harry's father, and Gaius could well imagine that the ghost really didn't approve of Sirius shagging Severus Snape's younger half-brother.
His surprise, however, registered as no more than a lift of one black brow, and he didn't break stride as he walked up to Sirius, wrapping his arms around his lover's shoulders and pressing against his body, greeting Sirius in the same fashion he would have if the ghosts hadn't been there at all.
"Hello, Liebling," he said, his voice a deep purr as he nuzzled his cheek against his lover's, then kissed Sirius lightly on the lips. "You're a sight for sore eyes. Ready for the Fair, then? I just need to change out of these robes and I'll be set as well."