A new pair of diffractometers arrives at the laboratory, and Professor Lexman is keen to put them to use. However, he soon realises that they won't work unless he can find a Welshwoman to help him calibrate them. He enlists the help of his students, but no one can seem to find the Welshwoman. Finally, he tracks her down to a pub in the town centre. However, upon arrival, he finds she has already left!