People-watching can be a pleasure, but it can also be dangerous and the lives we create for the observed and the tales told of them can run away with the teller. This is the dilemma for Jasper and Hebe Clavering while they are staying in the watering-place Oldenwells for the benefit of their elder invalid sister Luda. The children are fascinated by ‘the queerest-looking creature you ever saw in your life’. With the air of a boy detective Jasper announces, ‘I have my own ideas about her … but I’m not ready to tell you all about them yet.’

Eventually he can’t resist sharing his belief that the hobbling creature he has spotted down in the street is a witch. This sparks a revealing discussion between the siblings about witches. Hebe responds that it’s all nonsense. ‘There aren’t any things like that now – not fairies or mermaids or wood-sprites or those other things …[sirens] beautiful ladies who sang lovelily magic songs and that made people hunt about to see who was singing, and then they tumbled into the water and got drowned.’ This indeed reflects the changing fashions of Mrs Molesworth’s writing career where she had employed all of those traditions but they were no longer so popular or marketable in Edwardian times.

But Jasper convinces Hebe, despite his own horror of how the witches were treated ‘pitching them into the water to see if they’d drown, and horrible things like that. It was very wicked, of course, though the laws allowed it.’ Hebe confesses, ‘I’ve read something about it too. Some quite good, nice old women were treated like that. It was horrible.’ The way to spot them, as Jasper confidently announces, is that ‘They go in threes … at least generally.’ Remember those ‘in Shakespeare – and in my mythology – three Fates’.

Having spotted their first witch, the children need to find the remaining two witches. The perplexity for the children is about whether all witches are really ‘poor and beggar-like’? Or can they pass as ordinary woman – young or old, rich, or poor, hale, hearty or poor in spirit? How can the children find the other candidates because of course, as Jasper has explained, there has to be three.

This is only the beginning of their self-imposed quest and a thickening plot of shifting identities – there’s one they call ‘Cinderella’s godmother’ in her ‘Cinderella chariot’ or is she the one they call ‘Red Riding-hood’s sham grandmother” – the wolf one’? Eventually Luda herself is drawn into the guessing game. But the story is, of course, set in a sensible English spa town so any magic is of the ordinary everyday variety of a well-constructed plot and Mrs Molesworth’s amusing, determined and confused child detectives.