Derek Wainwright

In the short story In a Glass Darkly, Derek Wainwright is a man who the unnamed narrator thought was being attracted to his wife, Sylvia Carslake. The narrator's feelings of jealousy led to a breakdown of the marriage and Sylvia leaving him.

There is very little description of Wainwright in the story. The narrator describes him as someone who had everything he did not--brains, good looks and a witty tongue. He was "a thoroughly good chap" and, so the narrator thought, "just the man for Sylvia."

Portrayals
In the episode In a Glass Darkly of The Agatha Christie Hour, an TV film adaptation of the story, Derek Wainwright is played by Nicholas Le Prevost. Derek's background is embellished for the purpose of the dramatization. He is a doctor training to be a psychiatrist and would soon be going to Vienna for further training. He even offers to help treat Sylvia's husband for his (what we today would call) PTSD stemming from his war experiences. Derek has (non-canonical) a sister named Charlotte Hardy who introduces Derek to Sylvia. In the show Sylvia and Derek actually go riding together. He tells her that he is in love with her but she responds that she cannot go with him as she still loves her husband. This does not happen in the original story where much of the attraction between Sylvia and Derek might have been in the jealous imagination of the narrator.