A lot of times with magic, you'll find that your detection spells don't detect much of anything. Look for evidence of this, or that? There's none. Try to scrutinize a resonance? It's vague or confusing. Attempt to alter the environment? It resists change.
Infuriatingly it's when you're not expecting to find anything that you stumble upon everything.
Agnasci's spell seems to do very little at first, but there's a creeping sense of something being... off, that slowly overwhelms the mage. Penrose has told Agnasci that distance is an illusion: The hundred yards between him and the Gold Dragon are no more real than the hundred yards between two points in a video game. That's something the mind has difficulty accepting, but Agnasci's magic doesn't lie. The illusion of reality, of space itself, has slipped here. Agnasci immediately brings up Third Eye, but there's no magic to be examined, no traces of psychic powers. All there is are the ripples of a spell cast at some point earlier and Agnasci hones in on them, walking briskly away from the group toward a bench near the buffet.
It's very difficult for Agnasci to get his mind around, but there's a spot behind the bench that has, at some point in time, even if for only an instant, existed here and somewhere else. And not just one other place, but multiple other places. The fading resonances of other locations are all stacked on top of each other in this one spot behind the bench. The truth doesn't come to Agnasci immediately: Ever since awakening he's focused more on magic of the mind than anything else, but a mastery of space is his right as a Mastigos.
There have been multiple teleportations to the exact same spot behind the bench, all from different origin locations, over some amount of time that Agnasci can't guess at.
The other three mages look on in silence at Agnasci staring intently at the ground by the bench. The same bench where Harper found the doll. Where Harper and Law met Earnshaw.