Determined to solve the case, Lupin disguises himself as Prince Sernine and worms into the life of the Widow Kesselbach, whose billionaire husband was among the murdered.
The Chief of Police and his assistant investigate Madame Kesselbach's mysterious red-headed maid… and discover an underground passage leading from the outside.
Arrested as a murderer, Lupin works the Kesselbach case from jail. He masterminds the search of the home of a man who has tried to murder him - twice!
Fully aware of the Kesselbach affair, Kaiser Wilhelm II of Germany arranges to meet with Arsene Lupin.