This is a fun book.
The narrator, Mark Easterbrook, stumbles upon the existence of murderers for hire in 1960s London. When he finds an actual place with practicing witches in a house with the same name as the murderous society, he becomes suspicious.
Later, a conversation with a police medical examiner friend reveals the existence of a list of people taken down by a priest from a dying woman. The priest was killed moments after making the list.
The list turns out to be a list of people who recently died, of apparently natural circumstances, from an assortment of illnesses. In the local inn by the witch’s abode, the nephew of one of the dead people had been for a visit, about a month before she got sick.
Clearly, something is afoot.
He engages with the witches, claiming to be a man in need of freedom from a wife who won’t divorce him. But when his friend Ginger–playing the wife–starts getting seriously ill for no apparent reason, he starts to panic.
How do the witches do it? There is no physical contact between them and the victim and the only people Ginger saw were normal visitors–meter readers, handymen, and so on.
The answer is found in the work of consumer research firms and one consistent symptom, the loss of hair.
This is a clever little book, as indeed are most of Agatha Christie’s works. Unlike many others, there is no ongoing sleuth (there’s no Poirot or Miss Marple in this. Ariadne Oliver is in this one, but it’s not going to harm you to read this without reading other Oliver-involved mysteries.) so you can read it as a stand alone.