From the book:
The entire affair is shrouded in mystery, said D'Arnot. "I have it on the best of authority that neither the police nor the special agents of the general staff have the faintest conception of how it was accomplished. All they know, all that anyone knows, is that Nikolas Rokoff has escaped." John Clayton, Lord Greystoke—he who had been "Tarzan of the Apes"—sat in silence in the apartments of his friend, Lieutenant Paul D'Arnot, in Paris, gazing meditatively at the toe of his immaculate boot. His mind revolved many memories, recalled by the escape of his arch-enemy from the French military prison to which he had been sentenced for life upon the testimony of the ape-man.