Howard left three synopses of Gunman's Debt, with varying levels of detail:

The first synopsis introduces John Kirby, a gunfighter from South Texas, arriving in San Juan, Kansas. The town, awaiting a railroad, is a place of opportunity and conflict. Kirby's journey is motivated by a message from Billy Lynch, a friend tending bar in San Juan. This message, received in Ellsworth, prompts Kirby's visit, setting the stage for the unfolding events in the story. This synopsis sets the context for Kirby's arrival in San Juan but ends abruptly, leaving further details of the plot unexplored.

In the second synopsis of "Gunman's Debt," John Kirby arrives in San Juan to verify if his Texas feud rival, Jim Garfield, is dead. He encounters a marshal who disarms him and later faces Garfield, who reveals his plan to exterminate the Kirby family. A dance-hall girl, Joan Laree, helps Kirby escape, leading to a complex series of events involving betrayal, a murder falsely attributed to Kirby, and a multi-sided conflict. This culminates in a violent showdown, with allegiances shifting and the town facing near destruction.

The third synopsis of "Gunman's Debt" describes John Kirby's confrontation with Jim Garfield in the Silver Boot saloon, where he learns of Garfield's intent to destroy the Kirby family. Joan Laree, a dance hall girl, helps Kirby escape but then betrays him, thinking he killed Jack Corlan. The story unveils a complex plot involving Garfield, Blanton, and their feud with Kirby, leading to a final violent conflict. Joan's actions and the resulting three-sided fight end with significant deaths, leaving San Juan in flames and Kirby and Elkins forming an alliance.