Ah, the advantages of being a known mystery writer, so you can count on your readers. This is a rather unusually structured tale. Though you are warned in advance if you know enough about bells: Nine Tailors is part of tolling the bell for the dead.
It opens with Lord Peter suffering an accident in an out-of-the-way place, and finding himself (and Bunter) at a village in the fen country. As a consequence, he is able to help them ring the bells for the New Year -- a grand peal that lasts nine hours. Immediately after, the Rector has to go for a deathbed: Lady Thorpe is dying. Lord Peter hears of a tale of a crime, the theft of immensely valuable emeralds, which happened years ago, and the criminals were punished -- one died after a prison break -- though the emeralds were never recovered. On his way away from the village, Lord Peter meets a stranger on the way, who asks for directions. (None of which, you notice, points to something for Lord Peter to investigate.)
Sir Henry follows his wife a few months after, but when they dig up the grave to add him to it, they discover another corpse had already been added to it, and a great disfigured one, as well. The Rector is so bold as to write to him, since he had learned what sort of guest they had had. Lord Peter starts by testifying at the inquest, about the stranger he spoke with, though the real surprise there was the doctor, who said that the head blows had not caused the death, they had only disfigured his face, and he couldn't figure out what had. The corpse had been bound before death, but the head injuries had been inflicted after, as had cutting off the corpse's hands.
With that mystery before him, Lord Peter investigates. The emeralds figure. It involves children afraid to go past a graveyard, a deciphered message about as cryptic as the original, a letter from France to someone called Paul Taylor, a beer bottle that got dusted before it can be checked for fingerprints, a retreat during World War I, a burglar happening on a corpse, and much more.
Provides a particularly interesting view of ringing bells and the fen country, as well as the mystery.