From the first pages of the novel, the reader is bombarded with an avalanche of mysterious incidents, strange finds and amazing adventures, twisted by the authors into a tightly tightened knot. As fate would have it, the employees of the special laboratory receive a mysterious Indian dagger, the blade of which easily penetrates through any material, without causing harm to either the living or the dead. Where did this amazing weapon come from, what unknown danger was it forged against, and how did an unknown craftsman manage to achieve such amazing properties? Fantastic hypotheses, sea adventures, detective stories, the secrets of ancient India and the fight against dark forces make up the plot of this book, written by the classics of Russian science fiction. Published for the first time in 1961.