Kaname is in the doldrums: There's just one week until the end of summer vacation, and she hasn't done anything interesting! Fortunately, Sousuke is here to provide a little adventure, by offering her a trip to Merida Island. But what starts for Kaname as a simple trip to learn more about the mystery surrounding her quickly snowballs into a firefight in a chemical weapons facility, a reunion with a mortal enemy, and a battle for control of a runaway submarine! However things turn out, at least she can't claim that her summer was uneventful...