The Lost Sword

This is an Apple Books audiobook narrated by a digital voice based on a human narrator.

AN UNDERWATER CITY.
A MYSTERIOUS NINJA.
A MISSING SWORD THAT COULD CHANGE THE WORLD.
As the dark clouds of another war loom, Jack, Scarlet and Mr Doyle travel from the grimy streets of London to the vast neon - bright metropolis of Tokyo.
They're on a secret mission for the British government: to locate the Kusanagi sword, an ancient relic believed to have magical powers. If they can find the sword, the Emperor of Japan promises to keep the peace between his nation and the Allies.
But in Tokyo they soon discover that the Nazis are after the sword, too.
And they will stop at nothing to achieve world domination...