After surviving the harrowing ordeal of vampiric Jubokko trees and Gashadokuro's particularly insistent concerns about a haunted book, Clue is looking forward to enjoying her vacation. Spring Break has come for Hyperion Community College which means a week off for Clue, and she's made plans to enjoy it with Cosmo.

The two of them are partnering in Scorpius' Annual Spring Fishing Tournament in the billfish competition. With Clue as his partner, Cosmo is planning to win. Having the handmaiden to Palena, Goddess of the Ocean Waves, on his boat, he believes Clue will bring him the luck he needs to land a winning marlin. However, they aren't the only ones hoping to catch something.

The Fuguruma yohi who has been haunting Clue's books has been doing everything it could to draw her attention to a particular story in Tales of Plum Blossom Forest. It's the story of the farmer's second son, who left home to become a fisherman. Sadly, he was lost at sea, and the fishing buddies soon learn for themselves why.

When the Sea Harpy is swallowed whole by Bake-kujira, a ghostly whale, Clue has no choice but to must solve the mystery because their lives as they know them depend on it.