While Rumo is not a prequel to Bluebear, the two do have many parallel events and returning characters such as Volzotan Smyke, Professor Nightingale, and Fredda the Alpine Imp.
The first book chronicles Rumo's childhood, beginning with his puppyhood raised by Hackonian Dwarves, his capture and lengthy detainment by fearsome Demonocles on a floating island known as Roaming Rock, and his befriending fellow prisoner Volzotan Smyke.
Desperately in love with Rala but incredibly bad at showing it, Rumo leaves Wolperting to make a token to gain her favor but upon his return, he discovers an empty city and an entrance to the Netherworld.
Rumo must fight his way across the Netherworld and back to rescue his kinsman from the horrors of Hel and save his beloved from her seemingly deadly fate.
"[1] Colin Greenland of The Guardian wrote that Rumo "makes a perfectly appropriate, even charming object for the interest of the readers he is likely to attract" and called the novel "undemanding" yet "unpretentious, far from stupid, and demonstrably humane.