As with many kidnappers, they often send a messenger of some sort, and this is who arrives at Basil's door. His identity is revealed much later, but for now, he is only asked to deliver a note and depart as quickly as he came. Basil, meanwhile, learned a lot about the messenger just by observation along with bits of dirt left behind on the doorstep. From there he was able to take samples of the dirt to see where exactly this messenger came from and begin his journey from that point on.