Here is the subtitle of the book: A Romance Founded on Wagner's Operas "Rheingold," "Siegfried," and "Gotterdammerung."
The book is available at Hathi Trust and Google Books.
IN THE RHINE-DEEPS
THE BUILDING OF WALHALLA
IN THE UNDER-WORLD
THE CURSE OF THE RING
THE WOLSUNGS
IN THE SMITHY
A CONTEST OF WIT
THE WELDING OF NOTHUNG
BEFORE THE DRAGON'S LAIR
THE FIGHT WITH THE DRAGON
NEW ASPIRATIONS
WOTAN AND ERDA
BRUNNHILDE
THE NORNS
THE PARTING
THE GIBICHUNGS
THE CUP OF OBLIVION
THE BETRAYAL
A FATAL ERROR
A FURTHER BETRAYAL
THE END OF SIEGFRIED
THE END OF IT ALL