Nepenthe is a lush tropical island, which is unusual in the Barbaric Archipelago. Possibly it has heat from geothermal activity, or as later discovered, heat from dragons. The island has pristine white sandy beaches, and is specked with mysterious hot springs, with sedative properties.
Hiccup, Valka, and the Dragon Riders fly to the island of Nepenthe at a request for aid from Calder. The island is being wracked by earthquakes that have been getting progressively worse. The Riders make several startling discoveries, and ultimately Nepenthe and its people must start fresh in an altered environment.
In a nod to The Serpent's Heir, the game School of Dragons mentions Nepenthe in its expansion "Secret of the Leviathan". The expansion and the graphic novel were both released around the same time. It is possible that the emissary that Hiccup refers too is Calder, which would mean that the two take place at the same time, explaining why none of the Dragon Riders join the player on the journey to Impossible Island in the expansion pack.
- Nepenthe is a mythological Greek drug for sorrow and depression.
- Nepenthes is the genus name for a group of tropical carnivorous plants, commonly called "Pitcher Plants".