A circular plot structure is one in which story nodes are connected to other ones in a circle. Each node is connected to only one other story node, and the nodes are always visited in the same order.
A circular plot structure is defined by the fact that each of the story nodes is connected to only one other story node, yet they must go in the same order in the story. Depending on how long this story is, it may loop around through the same nodes multiple times. There is a variation on this structure in which there is a story node that is placed in the center of the diagram. An example of a circular plot structure that is often used in fiction is, "boy meets girl, boy loses girl, and boy gets girl back."