A subplot is a series of connected actions within a work of narrative that function separately from the main plot. Plot--the connection of events in a temporal or metaphorical line--is distinct from action (events themselves), and when a work of fiction has both a central plot and a second set of connected actions that is separate from that plot, it is said to have a subplot.

Subplots may connect to main plots, in either time and place or in thematic significance, but they cannot carry forward, strengthen, or explicate that main action. Subplots often involve supporting characters, those besides the protagonist or antagonist.

A subplot is sometimes referred to as a "B story" or a "C story" and so on, with the "A story," being the main plot.

Examples of works of fiction which contain a subplot:

• In William Shakespeare's Henry IV, Part II, the main plot concerns Henry's growth from "Hal" the prince to "Henry" the king and the reconquest of French territory. A subplot, however, concerns Falstaff's participation in the battles. Falstaff and Henry meet at several points, and Falstaff is a familiar of Henry's, but his plot and Henry's do not mix. Even though they may be thematically connected, they are not connected in action.

• In Anna Karenina by Leo Tolstoy, the main plot consists of the title characters’ attempt to leave her husband and find happiness and a decent social standing with Count Vronsky, but a subplot develops around Vronsky’s former love, Kitty’s reconciliation with Levin, a farmer who once attempted to court her.

• In The Great Gatsby by F. Scott Fitzgerald, the main plot consists of Gatsby’s attempt to gather the admiration of his old love, Daisy but a subplot develops concerning the romance of their friends, Nick Caraway and Jordan Baker.

• In Catch-22 by Joseph Heller, the main plot consists of U.S. Army Air Corps Captain Yossarian’s attempt to avoid dying in World War II, but a subplot develops around mess hall officer Milo Minderbinder’s rise as a king of a black market food trafficking.

• In Goodbye, Columbus by Philip Roth, the main plot consists of the romance between Neil, a twenty-something slacker, and Brenda, a suburban princess, but a subplot develops around an African-American child who loves art books and who Neil observes at his job in the public library.