The Adventure of the Lion’s Mane by Arthur Conan Doyle. Short summary

5 seconds

The teacher dies a strange death. There are marks on his body, as if from numerous whiplash blows. Holmes discovers that the man was killed by the poisonous jellyfish «Lion’s Mane».

1 minute

Retired Holmes lives in a remote villa in Sussex and befriends the local school principal, Stackhurst. One day, before their eyes, schoolteacher McPherson dies on an empty beach. His body is horribly scarred, as if the man had been beaten with a whip. Before he dies, he utters: «A lion’s mane.»

Another teacher, Murdock, is suspected of the murder. He has an explosive temper, and the dead man stole his bride. But as Holmes and the local inspector discuss the possible guilt of Murdock, he is brought in by the principal in a semi-conscious state. The teacher has the same wounds on his back as MacPherson. With great difficulty, Murdock is saved.

Holmes guesses that such wounds can be caused by the poisonous jellyfish Cyanea or Lion’s Mane. The inspector, Holmes and Stackhurst find it in the bay and kill it.