Another theme could be trust. Since there is a secret involved, it's likely that the concept of trust among the characters is explored. For instance, if a character discovers another's secret, it could break the trust between them. Or perhaps the story shows how difficult it is to trust someone when you suspect they are hiding something. And also, the theme of discovery could be there. As the story unfolds, the discovery of the secret could be a major plot point, leading to changes in the characters' lives and relationships.
The theme of identity might be present in 'the secret short story'. The secret could be related to a character's true identity. Maybe a character has been living a lie, and the secret is about their real self. This could lead to themes of self - acceptance and the search for one's true place in the world. For example, if the secret is that a character is from a different social class or has a different heritage than what others believe, it can cause internal conflict and external challenges as they struggle to either keep the secret or reveal it and face the consequences.