A telepathic recorder was an jewel-like object or device that was essential to Vespiforms, containing part of their mind. It could be imprinted by intense and emotional thoughts, even by humans, and thereafter contained a sort of essence of personality or motivation to guide the Vespiform.
Vespiform had a strong tendency to keep their telepathic recorders close, even if that meant that they would havve to enter a dangerous situation, and if the telepathic recorder was destroyed, the Vespiform died as well.
One of these recorders was brought to Earth by a Vespiform known as Christopher. After its death in 1885, the recorder came into the hands of his lover, Clemency Eddison, who assumed it was a jewel and took it back to England, naming it the Firestone. Its jewel-like qualities were apparently impressive enough to attract a thief, the Unicorn.
In 1926 Christopher's son, Arnold Golightly, who had been locked in human form all his life, took on a Vespiform form for the first time due to intense anger. He promptly made contact with the firestone, which imprinted in him the mindset of an Agatha Christie-style killer, because Lady Eddison, the wearer of the firestone, was at the same time musing on the amazing plots of her books.