Twenty-first in the long-running mystery series with Dr Launcelot Priestley. >Famous research chemist Bernard Threlfall is found dead and his laboratory ransacked. He had also been about to change his will, potentially giving his relatives motives for his death. The case is extremely tricky, providing a test for both the different detecting styles of the new Hendon graduate Inspector Waghorn and the more traditional Superintendent Hanslet. Ultimately both are forced to turn to the genius of Professor Priestley to solve the puzzle.

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