Professor Philip Mortimer is going to Cairo, Egypt for a holiday. He soon gets mixed up in a weird business with ancient papyrus, heretic kings, lost treasures, an old nemesis, and the murder of his friend; Captain Blake.

For some time now London has been terrorized by an enigmatic villain who informs the press in advance of his crimes. He commits daring robberies and leaves behind an "M" in a yellow circle as a signature. When the Imperial State Crown is stolen from the Tower of London, the Home Office assigns Captain Francis Blake to assist Chief Inspector Glenn Kendall of Scotland Yard. Blake in turn calls in his old friend and housemate, Professor Philip Mortimer, who has been on holiday to Scotland but agrees to return to London to help in the enquiry.

The world’s weather has gone mad, Professor Mortimer responds on an invitation of his friend Professor Labrousse, while travelling to his friend, Mortimer's cab crashes and he finds himself a new adventure right on his friends doorstep.

When Mortimer discovers a time machine built by his old adversary Dr. Miloch, he can't resist to try it out and travels through time to a prehistoric swamp, the Middle Ages, and a desolate wasteland in the 51st century.

A dragon has been seen in Japan and Mortimer visits his old friend Professor Sato to find out what's going on

Scandal breaks in the London press: There is a mole in the Intelligence Service! And it appears without a doubt, on a photograph taken by agents of MI 5, that the mole wears the face of Francis Blake! Mortimer is determined to believe that his friend has been forced to act against his will. But the initial investigations sweep away this hypothesis: Blake has opened, under an assumed name, an account fed by payments coming from the Bahamas. In a few months, he has withdrawn ₤30,000—more than 10 times his annual pay! With MI 5 agents planning to try Blake for high treason, or to kill him if needed, Mortimer decides to find his friend before they do. A long hunt begins …