Sylvia Carslake

In the short story In a Glass Darkly, Sylvia Carslake is the younger sister of Neil and Alan. She was engaged to Charles Crawley, but she broke off the engagement.

Sylvia has "vivid golden hair", and a "lovely face".

During the narrator's first visit to Badgeworthy, he sees a vision of a woman being strangled, whom he later realizes is Sylvia. He tells her about it, and she tells him that she believes him. A week after that, she breaks off her engagement to Charles Crawley.

After Neil is killed during the war, the narrator has to tell Sylvia about his last moments. She had adored Neil, and is described as being "adorably sweet" in her grief.

The narrator later tells Sylvia that he loves her, and she tells him that she had fallen in love with him when she first met him, which was why she had broken off the engagement with Charles.

Sylvia and the narrator later get married, and he is devoted to her, but also jealous. She is amused at first, but later begins to withdraw from him emotionally.

After Sylvia and the narrator meet Derek Wainwright, he thinks that Derek is the man for Sylvia, and becomes even more jealous. He lets loose at her one day, with "a string of savage, unwarranted abuse". She then leaves him, leaving a note saying that she is going to Badgeworthy and then to the one person who loves and needs her.

The narrator follows Sylvia to Badgeworthy, and begins to strangle her, until he sees their reflection in the mirror and realizes that this is the vision he had seen on his first visit to Badgeworthy. Sylvia comforts him when he breaks down, and explains that when she mentioned the person who loved and needed her, she had meant her brother Alan.

Portrayals
In the episode In a Glass Darkly of The Agatha Christie Hour, an TV film adaptation of the story, the part of Sylvia is played by Emma Piper.