I'm not terribly familiar with the post-Sayer canon (or some of Sayers' later works) but then apparently this story diverges anyway. It's a thoughtful character study of Saint-George and his viewpoint on Harriet and Peter.

A Clean Fire (1359 words) by harborshore
Chapters: 1/1
Fandom: Lord Peter Wimsey - Dorothy L. Sayers
Rating: General Audiences
Warnings: No Archive Warnings Apply
Relationships: Harriet Vane/Peter Wimsey, Saint-George Wimsey/OMC
Characters: Saint-George Wimsey, Peter Wimsey, Harriet Vane
Summary:

Saint-George grows up.