Another theme might be the passage of time. Vaulted halls that are entombed often give a sense of a place that has been forgotten and left to the ravages of time. It could explore how time changes things, both physically and in terms of the memories or stories associated with the place.
A theme of mystery could also be present. The very idea of vaulted halls being entombed implies something hidden or unknown. There could be secrets within those halls, and the story might revolve around the characters trying to uncover these mysteries, whether they are related to the history of the place or something more supernatural.
I'm not sure as the title alone doesn't give much information about the characters. It could be a lone explorer who stumbles upon these vaulted halls. Maybe someone who is on a quest for knowledge or treasure and is the first to penetrate this entombed place.
Perhaps ancient artifacts or lost knowledge might be found there.
Maybe it's associated with a group of early settlers. They could have built the vaulted halls to preserve their origin story, which was then entombed within. It might be a way for them to safeguard their heritage from invaders or the passage of time. The halls could be filled with items that represent their first days in the area, like tools they used, or stories written on primitive parchments.
It could be about time, as the numbers might suggest something related to a specific time like December 1st. Maybe it's about missed opportunities or new beginnings associated with that time.
It could be about love. Love is a very common theme in short stories, like a short-lived romance or unrequited love.
One possible theme could be isolation. The telephone man might be isolated in his work, constantly dealing with machines rather than people on a personal level. Another theme could be progress. Since he's involved with telephones, which are a form of technology, the story could show how technology is advancing and how he either adapts or struggles to keep up. Also, connection could be a theme. He is the one who helps people stay connected through telephones, but he himself might lack certain connections in his own life.
The possible themes could be love. Maybe it's a story about a young couple falling in love and facing various challenges. It could also be about friendship, like two friends going through a tough time together and coming out stronger. Another possible theme is self - discovery. Gertrude might write about a character who embarks on a journey to find out who they really are.
One possible theme could be change. Since it's 'after the hook', something has already happened to disrupt the normal state, and the story could be about how the characters or the situation changes as a result. Another theme might be discovery. Maybe the hook was the start of a journey of discovery, and the theme is about what is found or learned after that initial moment.
One possible theme could be redemption. Maybe the main character has made mistakes in the past and through the course of the short story, they strive to make amends.
One possible theme could be finality. Since it mentions 'the end', it might be about the end of a relationship, a journey, or a life. And if 'blythe' is related to a character, then the theme could also involve how that character copes with the end.