Sherlock Holmes – In Pursuit of the Tetragram. Sherlock Holmes, #6

Sherlock Holmes is back in an unpublished case that will change everything you thought you knew about him. When a professor of cryptology is found murdered outside the British Museum, his dying message sends Holmes and Watson on a breathless chase across four continents. The clue: an ancient symbol called the Tetragram - four letters, four elements, four cities. Egypt, Jerusalem, Rome, Trier. But these are only the first four pieces of a puzzle whose fifth element is a forbidden melody: the Lost Melody.
From the foggy streets of London to the catacombs beneath Rome, from the Temple Mount to the iron gates of Trier, Holmes unravels a conspiracy that reaches far beyond a single death. The mysterious "Dark Pharaoh" is always one step ahead. And the deeper Holmes digs, the more he realises that the greatest secret is not a treasure, but a terrifying truth: knowledge unshared becomes poison. Joined by a brilliant but haunted assistant, a fearless countess, and a virtuoso violinist, Holmes must assemble the four fragments of the Tetragram before the Dark Pharaoh unleashes a power that could reshape the world - or end it.
This is the adventure Holmes and Watson never wanted to publish. Over of suspense, riddles, history, and music. A novel for every lover of classic mystery, arcane symbols, and the enduring friendship of Baker Street's greatest duo.