In the foyer of a Paris hotel, Mortimer joins up with his friend Blake to deliver startling news: his old adversary, Dr. Miloch, recently deceased from radiation poisoning, has bequeathed him a scientific discovery, hidden inside a house in La Roche-Guyon.

A taped recording of Miloch's voice gives him instructions of how to use the time machine, and once inside, Mortimer activates the device, which stuns him into unconsciousness as it takes off with gut-wrenching velocity.

Mortimer narrowly escapes the dangers of the prehistoric swamp and into the future, where he finds himself inside the castle which is connected to Miloch's house via a secret passage, witnessing a violent peasant revolt against the tyrannical lord, Baron Gui de La Roche.

However, a tyranny system eventually established itself from a remnant of civilization, rising to supreme power over the world and attempting to completely subjugate humanity as a slave race under its rule.

A rebel movement has arisen despite the strict surveillance of public life and allied itself with human colonies spread all over the solar system, and Mortimer's accidental arrival in the future inadvertently "confirmed" a prophecy that a red-bearded liberator would one day appear to cast down the tyranny and lead the oppressed to freedom.

As Mortimer travels back, he finds that the acceleration does not affect him anymore due to his protective suit, and thus he manages to stop the time machine a few weeks before his departure from the present.

As he arrives several days afterwards - to a point where Blake has since begun searching for his missing friend - an explosive booby trap left by Miloch as a final insurance destroys the chronoscaphe and the laboratory, though Mortimer ultimately survives because of his suit.