Take it up with the library management, Strange, or whoever the fuck decided to cast Lambert as the protagonist here. The fabric of the story, if nothing else, seems to accept the existence of a fae servant without a hitch. Now, what was it Strange had said he needed ... ?

"All right, so I've got three things for you to do." Looking down at the items still clutched in his hands, he grimaces, then glances at Strange.

"You know, it kind of doesn't make sense to give this to Childermass without any explanation about what it is, does it? Isn't there a note to give him too?" Yes, yes, he knows that's how it apparently happened, but if Strange thought he wasn't going to criticize crazy Strange's plan while he was at it...