Some Must Watch is a novel by Ethel Lina White, first published in 1933. The book is a thriller/mystery that tells the story of a young woman named Helen Capel (the same name as the protagonist in “The Spiral Staircase”), who takes a job as a live-in assistant at a remote mansion in Wales.

As Helen settles into her new job, she becomes aware of a series of mysterious and terrifying events that are happening in the mansion. A young woman who worked in the house before her disappeared under suspicious circumstances, and Helen begins to suspect that someone is stalking her.

As the tension builds, Helen becomes increasingly paranoid and fearful for her life. She discovers that several people in the house have secrets and motives that could be connected to the mysterious events. Helen must use her wits and courage to unravel the mystery and stay alive.

Some Must Watch is a classic suspense novel that is often praised for its atmosphere and strong characterization. The book was adapted into a film called “The Spiral Staircase” in 1946, although the plot of the film is somewhat different from the novel.