That really doesn't surprise me as he can be prone to be, ah, scatterbrained (to put it kindly) about his personal (and other people's personal) possessions. I think its likely he spent it and forgot about it.
However, as things go in this household, when something is missing, we go to the kiddos.
"Boys, did any of you pick up a $10 bill you may have found laying around?"
Solemn faces, "no."
Ok, fair enough. We asked, they answered, my mom alarm didn't go off, so they are in the clear. (and, like most moms, I can tell when they are lying. They're pretty terrible at it.)
However, Ian has become my little story teller. He likes to participate in conversations by claiming he has performed the activity being discussed or owns the item currently being spoken of, or is "best friends" with whomever the conversation is about. He does it with a perfectly straight face. He is a classic "one-upper."
So, after the quick little mass interogation, he comes into the room, slides onto Tio Sabi's lap and lays this one on us:
"Sabi, Zacky took your money. I hear his mind say so."