Librería Samer Atenea
Librería Aciertas (Toledo)
Kálamo Books
Librería Perelló (Valencia)
Librería Elías (Asturias)
Donde los libros
Librería Kolima (Madrid)
Librería Proteo (Málaga)
The story is set in 1888. The SIGN OF THE FOUR has a complex plot involving service in East India Company, India, the Indian Rebellion of 1857, a stolen treasure, and a secret pact among four convicts ("the Four" of the title) and two corrupt prison guards. It presents the detective's drug habit and humanizes him in a way that had not been done in the preceding novel.