The Thumb Mark of St Peter | The 13 Problems | Miss Marple | Agatha Christie

About The Thumb Mark of St Peter

The Thumb Mark of St Peter is a short story in the collection The 13 Problems written by Agatha Christie. The story features an amateur detective Miss Marple, her nephew Raymond West, and her friend Sir Henry Clithering.

The victim of rumours

The final story to be told at the regular meeting of the Tuesday Club comes from Miss Marple herself. It concerns a niece of hers called Mabel who obstinately married Geoffrey Denman when she was twenty-two, despite Denman having a violent temper and a history of insanity in his family.

Ten years later he died, and Miss Marple wrote to offer to stay with her niece for a while, but received a reply back that politely refused the offer. Three months later a second letter was sent to her aunt hysterically begging her to come. Arriving at her niece’s house, which Mabel shared with two servants – hers and a nursemaid for her mentally-ill father-in-law – Miss Marple learned that the widow was the subject of gossip to the effect that she had murdered her husband, and no one in the area would now talk to her.

 Geoffrey had been taken ill in the night and died soon after the doctor arrived, but the old locum had not raised the alarm about the manner of death. It was thought that he had died after eating poisoned mushrooms. The two servants told Miss Marple that Denman had been unable to swallow and was rambling before he died about fish. An exhumation order was granted, followed by an autopsy that proved totally inconclusive. Miss Marple began to wonder if Geoffrey had committed suicide and used a knowledge of medicine gained in a previous period of his life to do so.

Thumb mark of St.Peter

Totally stumped by the problem, she was in the high street and in something of a silent prayer for guidance when she opened her eyes and saw a fresh haddock in the fishmonger’s window with its characteristic black spots known as the “thumb mark of St. Peter”. She realised that the solution lay in the mysterious words uttered by Geoffrey as he lay dying.

The Eye solution

Questioning the servants further, they stated that the words were to do with a “heap” or “pile” of some fish whose name probably began with “c”. Checking a list of poisons, Miss Marple found one called Pilocarpine and read that it is also an antidote for atropine  poisoning. Based on her own eyedrops, which contain atropine sulphate, she confronted the elderly Mr Denman and accused him of murdering his son. The insane man laughingly confessed the crime, committed because he overheard that his son was planning to put him in an asylum. He emptied his eye solution into his son’s bedside glass of water knowing Geoffrey would drink it during the night. Mr Denman is committed to an asylum after all and the Tuesday Club congratulates Miss Marple on her success, although Raymond points out there is one thing she doesn’t know. His aunt corrects him – she knows that he proposed to Joyce earlier in the evening!

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