"Riposte in Tertio" unfolds around the fascinating tale of Rosa Millard. Her schemes involve the cunning falsification of documents, leading to the repeated sale of the same horses and mules back to the unsuspecting Union army. In this intricate web of deceit, Ab Snopes plays a crucial role by assisting Granny. However, he slyly siphons off a portion of the profits from the stock sales for himself. As the Union forces prepare to withdraw, bringing an end to their unscrupulous enterprise, Ab betrays Granny, luring her into the clutches of Grumby, a rogue posing as one of Bedford Forrest's men, but in truth, a ruthless bully, thief, and murderer.

Despite the growing mistrust from Ringo and Bayard towards Ab, Granny is seen as a folk hero, a Robin Hood who has given much to the impoverished. Yet, in her grandiose efforts, she neglects to support John Sartoris, who desperately needs resources to restore his dwindling fortune. Tragically, Granny's avarice becomes her downfall, leading to her untimely demise. Her moral decline escalates, overshadowing even her charitable deeds for the needy.