As Nami has fallen seriously ill, the Straw Hats head to Drum Island in search of a doctor. However, they learn that there is only one doctor left on the island, the reclusive Dr. Kureha who currently resides at the top of a mountain. With a sick Nami in tow, Monkey D. Luffy and Sanji set out on an arduous journey to seek her help.

Meanwhile, the return of Wapol—Drum Island's former king—and his brother spells trouble for the island's inhabitants. As the one responsible for the current lack of doctors, Wapol has finally returned to take back his position as the people's despot and absolute ruler.

With the help of new allies like the half-human reindeer Chopper Tony Tony, the Straw Hat Crew must overcome all the obstacles in its way to save Nami's life and stop Wapol from plunging Drum Island back into tyranny.