The walls of the City only resonate with the incredible exploits of the "Yellow Mark". This mysterious criminal multiplies the spectacular actions: raid on the bank of England, theft of the Gainsborough of the National Galery, and even the theft of the Royal Crown of England... Nothing seems to be able to stop him. His daring goes so far as to warn the police of the place of the completion of his packages, ridiculing each time a little more Scotland Yard. The apparent ease with which he dislodges from the police devices ends up worrying the highest authorities in the country. Captain Francis Blake is sent by the Home Office to Scotland Yard to elucidate the case and discover the identity of the man who hides behind the Yellow Mark. The captain immediately associates himself with the services of his old friend, Professor Philip Mortimer, whose scientific knowledge will prove valuable in this extremely complex case. But here are the flights succeeding the abductions. A reputable doctor, a character-club will have an evil list of his own, a character--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------