One Piece, Volume 15: Straight Ahead!

Nami's sick! Now the  Merry Go  is without her navigator! Luffy and crew have but one choice--find land and hopefully a doctor. They miraculously stumble upon Drum Island, where it is eternally winter, but upon arriving they find out the island has only one medical professional--and she's a witch! With Nami's life on the line, Luffy sets out through the snow-laden fields to find this doctor, witch or not!