STANSTED, England—In a stately Victorian mansion, Julie Grist is teaching the psychics of tomorrow how to speak to today’s dead for a living.

Ms. Grist, a 66-year-old who says she has been communicating with the deceased for decades, explained the goal of psychic “reading” to a dozen first-time students from Europe, Asia and North America. Psychics mustn’t depress or frighten, she said, with unsettling predictions from the spirit world.

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