When a number of eminent scientists - all experts in their field, and of inestimable value to the British Government - mysteriously vanish, the police are at their wits' end. The only clue in each instance is a note left by the scientist saying they have joined 'the Green Mandarin'. Desperate to locate his daughter, Fleurette, a Home Office official enlists the services of scientific detective Ray Ellis. But as his investigations get closer to the truth, will Ray be the next person to go missing?