Several generations of his family live under his roof; his two sons, their wives and two young grandchildren, his young second wife Brenda, sister-in-law Edith and the children’s tutor Lawrence. It is indeed a crooked house, much like the nursery rhyme, since each resident has a very warped interdependence on the others. Charles Hayward is a young man who wishes to marry Sophia, the oldest granddaughter. He is charged by Sophia with finding the killer, since his father is chief of Scotland Yard.
Everyone stands to gain financially from the murder, since they are all beneficiaries. But there was no need for the step, since the old man would have gladly given them anything they asked for. Charles uncovers several secrets, like the failed business of the older son, the travel plans of the younger son and the supposed affair between Brenda and Lawrence. Further muddying the waters is the revelation that Aristide has re-written his will leaving everything to Sophia.
Shortly after, Josephine, the youngest grandchild who claimed to know the killer, is assaulted. Based on the revelation of the affair, Brenda and Lawrence are arrested. But after the arrest, the nanny is poisoned. Edith, the elderly lady takes Josephine out for ice-cream and drives over a cliff, killing them both. In a letter, she reveals that Josephine herself was the killer, and staged her own assault to throw the scent. Apparently she wanted to hurt her grandfather for not paying for her ballet lessons.
The whole premise was a little unsatisfying. Crooked they may be, but to have failed in the upbringing of their child to the level where she murders multiple people for attention seems far-fetched. Also, despite the efforts of the investigations, it seems like the solution pretty neatly falls into the lap of the authorities, rather than through their own efforts. Not her best work.