In London, professor Philip Mortimer, fatigued and suffering from memory problems since his experience in the sarcophagi of Açoka, is recommended by his doctor to rest.

On his return home, Mortimer immerses himself in reading his memories and discovers that the writer and amateur archaeologist Sarah Summertown, with whom he had an adventure in his youth, is a friend of the Leakys.

In the archives of the Daily Mail, a mysterious man manages to consult the article on Prof. Heidegang by posing as Mortimer's assistant to Mr Stone.

In the plane, Sarah talks to them of artifacts engraved with the same enigmatic signs found in the four corners of the world, which could indicate the existence of a civilization at the time of the unique continent of Gondwana.

Meanwhile, the mysterious man is handed a passport, a plane ticket to Nairobi and cash by David Honeychurch, who has received these instructions from his superior Blake.

The young woman now faces a pack of African wild dogs and is saved by shots fired from an airship where she recognizes Olrik without believing it.

The next day, Mortimer, Sarah, Nastasia and Bombo arrive at the Ngorongoro crater and plunge into the lake to find the secret entrance, not knowing that Olrik and Razul are right behind them.

They find themselves in a huge room with an extraordinary machine and Life explains to them: more than 300 million years ago, a civilization developed like theirs, but before the tensions engendered by growing injustices, scientists created an incubator to spawn new individuals if humanity were to disappear, which eventually happened.

All of them board the seaplane of Lord Archibald Mac Auchentoshan, a billionaire protector of nature, which carries the Açoka sarcophagi found by Professor Labrousse in the ruins of the Indian Antarctic base.