The facts are these:
- The hero is the Earl of Shane.
- Midway through the story, two people described as "the Earl's aunt-in-law and her son, his cousin and heir" show up.
- The Earl calls his aunt "Aunt Almeria." The story refers to her otherwise as "Lady Wilfrid Drayton" or just "Lady Wilfrid".
- Her son is called "The Honourable Frederick" and "Mr. Drayton".
I cannot square these facts with one another in a manner satisfactory to myself.
Relying upon my usual source for regency title information, I can see that Aunt Almeria's courtesy title of "Lady Wilfrid Drayton" means that she must be married to Lord Wilfrid, and that Lord Wilfrid must be the younger son of a duke or marquess.
How, then, is her son the Earl's heir? The younger son of an earl is not "Lord Firstname", so her husband's father must not have been an earl.
I also cannot find how the son of a younger son of a duke or marquess is addressed. I am perfectly ready to believe that they are called "the Honourable", but I cannot find any source to that effect.
Here are the explanations for the facts that occur to me:
1. The Earl's father, though he goes unmentioned in the story, is actually still living and is a Marquess. The Earl is the only son of the Marquess. Almeria married the Marquess's younger brother, Lord Wilfrid. Mr. Drayton is thus the previous Marquess's male-line grandson and so, if the current heir to the Marquessate dies without a son, he will sooner or later inherit the whole shebang. The Earl is 33, so it certainly conceivable that his father has not died yet, even back then. (This is the solution I prefer if it works.)
2. Lord Wilfrid Drayton was the Earl's mother's brother. The two had at least one older brother, who is the current duke/marquess. Lord Wilfrid's son Frederick thus has no real claim on the Earl of Shane's fortune, but for whatever reason, he is the person named in the Earl's current will. Obviously, Mr. Drayton would not inherit the title. Either the Earl's title would go extinct at his death, or it would devolve upon some distant relative to whom the Earl feels no responsibility to leave any of his money and land (probably the former). (I don't really like this solution, as it seems messy and might require me to learn all kinds of nonsense about regency era wills.)
3. Georgette Heyer screwed up. (This would make me sad.)
I have looked through Wikipedia pages on courtesy titles and the chinet.com pages, and tried to Google, but I haven't found much. Especially on the question as to the courtesy title, if any, of children of younger sons of dukes and marquesses. I can't find a word on that issue.