Important events in a novel serve to introduce and develop the plot.
In Avi's The Man Who Was Poe, after Edmund's sister, called Sis, goes missing, which is the central conflict of the story, one of the most important events is the moment Edmund meets Edgar Allan Poe and asks for his help. Without Poe's assistance in solving the mystery, there would be no further plot.
Other important events are when Poe discovers clues. For example, Poe and Edmund find a wooden plank and a button from Sis's shoe in the room of the building next door, which are important clues to help Poe conclude that Sis was kidnapped and forced across the plank from one room to the next through the windows. Later, in the Providence Bank vault, after the gold robbery, Poe is shown a button that also came from Sis's shoe and discovers a piece of string on the floor of the vault. When Poe compares the string to the bell ropes in the bell tower of the Unitarian Church, Poe concludes the string is really a piece of strong rope, and the rope was used to lower Sis into the vault through the air vent to help her kidnappers steal the gold.
Other important events help develop the resolution of the story, including Edmund finding his mother at the Unitarian Church and working with Mr. Throck to chase after his sister and her kidnappers when they are at sea.