Ash and friends spot their ninja friend Sanpei and his Greninja floating down a river, unconscious! After they mount a rescue, Sanpei explains that he’s on a mission for his ninja master, Saizo, but a masked ninja and his Barbaracle partner keep trying to interfere.

The gang decides to help Sanpei on his mission, but soon Ash and Sanpei are separated from the others—just as the masked ninja strikes again! Froakie and Greninja team up to fight him off, and when the battle seems to be going against them, Froakie evolves into Frogadier!

The masked ninja then directs Ash and Sanpei to the manor where their friends are waiting. There, they discover their pursuer is none other than Saizo, who has been using their encounters as a test of Sanpei’s skills—and Sanpei has passed with flying colors! With everyone safely reunited, Ash challenges Sanpei to a battle, and soon our heroes are off once again to Coumarine City.