This episode features Dr Thorndyke, played by John Neville, who is first a medical man and second a solver of mysteries. A young girl has been murdered in her boarding house and the solution looks obvious - but is it?
Professor Van Dusen, the 'Thinking Machine', boasts that he can think his way out of a prison cell. When he is locked up he is given the chance to prove that he can escape by the power of his mind alone.