One Piece (Omnibus Edition), Vol. 4

There's something fishy going on in Nami's hometown that's led her to turn her back on her family and friends. But her betrayal is all for naught when the unscrupulous captain of the fish-man pirates, "Sawtooth" Arlong, goes back on his word. When her fellow villagers gear up to challenge a merciless foe who can easily crush them, her only hope for peace is to turn to the very people she has been lying to… the Straw Hat Pirates!

One Piece (Omnibus Edition), Volume 4 — collecting manga Volumes 10-12 — by Eiichiro Oda.