The case of Alexander Litvinenko who is alleged to have been poisoned with thallium reminds Dr Grumble of the story of Georgi Markov. Georgi was a Bulgarian who defected in 1969 and settled in London. In the late 1970s he turned up at a hospital where Dr Grumble used to work claiming that he had been shot in the thigh with an umbrella. He was extremely ill and clinically it appeared that he had septicaemia. Within a day or two he was dead.
The tiny bullet which killed Georgi.
Just half a milligram of ricin (about the size of a pinhead) can be fatal.
The orginal reports carried in The Times can be read here. And here you can find an interesting interview with Annabel Markov, Georgi's wife.
Dr Grumble is dismayed that, though the cold war is long over, these things still seem to be going on.