The Grémillet sisters are staring down a cold and rainy week at the beach... But as they soon find out, even the drabbest of places can hide marvels!Sarah, Cassiopeia, and Lucille have stumbled into another adventure, this one prompted by a secretive ancestor, a rumored pirate treasure, and a beached whale... The biggest mystery, however, might be little Lucille, who's behaving more oddly than ever. As the trio follows the trail of clues before them, will they be able to overcome their differences and discover the truth? Little do they know, but the clock is ticking...