The sound of music from the basement was what drew his attention. Gibbs was often down there, but it was usually fairly quiet. Anna had left recently, and Marian and Katie were both sleeping peacefully. He'd sat with them for a while, to reassure himself more than anything, but he knew that thanks to Anna, they were both well.
Things hadn't ended well between he and Gibbs the last time, but he couldn't deny feeling a certain connection with the man, if only because he had understood him so well, and so quickly. Curiosity at the origin of the music had him slowly descending the stairs, hand on the railing, stopping at the bottom when he saw Gibbs. It was clear enough something was on his mind. And he knew that look in his eyes. It was not anything good.
He simply watched the older man for a moment, not saying anything. He knew that Gibbs knew he was there anyway, there was no reason to announce his presence.