With the Sinnoh League behind them, Ash, Dawn, and Brock head back to Twinleaf Town on a ship. A crisis emerges when, While following the ship in their submarine, Team Rocket anger a group of Tentacruel and the Pokémon soon attack the ship. Although they try to hold them off, Pikachu and a bunch of young Pokémon become sick with poison. A bigger problem arises the ship's captain reveals that the ship does not have an infirmary and there are no doctor or nurses on the boat. Nurse Joy is contacted, but she will be unable to get to the ship for two hours. With no one else to help, Brock is the only one who can help those Pokémon.