A fabulous diamond in a museum, known as "Nell Gwynn's tear" is pronounced a fake by a mysterious woman, but when it's authenticity is out of doubt, Fabian is put on the trail of a forger.
Ken Masters hides in the Eygptian room at the Warwick Musuem and takes a number of uncut diamonds. The only clue is a thread from a tweed jacket. Fabian is tipped off and learns Masters is a poet and his family live in desperate poverty.