Ritter later describes being kept in a grand, flooded house that was filled with statues for roughly two years. Laurence was involved with suspicious disappearances and was eventually arrested for kidnapping a young man, James Ritter. He learns that a man named Laurence Arne-Sayles (who later turns out to be the Prophet) had a group of students, including Val Ketterley, with whom he'd discussed a 'grand experiment' - a different world featuring architecture merged with oceans. (Later, the Other tells Piranesi should not speak to '16' or else he'll go mad.) Afterwards, Piranesi starts reading through the earliest entries in his journal, none of which he remembers writing, and looks up some of the names the Prophet had mentioned. He also says that the Other's real name is 'Val Ketterley' and that '16' is looking for Piranesi. The Prophet says that this World is created from ideas from a different world. In Part III, Piranesi comes across an old man, who he nicknames the Prophet. One day, the Other tells Piranesi that someone (who they nickname '16') may show up, but that '16' is their enemy.

Piranesi also forgets things and loses track of time, but the Other does not. The Other, however, is able to procure things like blankets, shoes, etc. Piranesi survives by fishing, gathering seaweed and collecting fresh water from waterfalls. Piranesi helps him with this research, but he doesn't really believe in it. The Other believes that the labyrinth contains a Great and Secret Knowledge. Part II, Piranesi meets with the Other, the only other living person there. The lowest level floods continuously, and Piranesi has located the skeletal remains of 13 dead people in the labyrinth. Part I introduces Piranesi, a man who lives in a grand, 3-tiered labyrinth, filled with statues.

Piranesi by susanna clarke