Summer vacation has finally arrived! And like every year, Sarah, Cassiopeia, and Lucille are off to the peaceful little village where their grandmother lives. There they'll find their old friends, the sleepy countryside, and... a ghost! Indeed, a mysterious presence haunts the ruins by the lake. Where does it come from? And why does it ring the bell in the old church? Finding out will be the new mission for the Three Sisters' Club! But to unravel this mystery, they will have to travel back in time, meet fair damsels and knights, and confront tortured love stories past and present...