The Mind Readers (1965)
My review:
One of Allingham’s few (mercifully few) outstanding balls-ups. The plot is a mess, with a lot of needless complications (all recounted in Allingham’s obscure vein that makes Gladys Mitchell look sober and straightforward) failing to disguise the fact that there is no actual plot to speak of. The murderer is known very early on, revealed and killed some chapters before the end, which is an anti-climax rivalled only by the behaviour of Albert Campion.