The Strange Sound by the Sea by Haley Stewart

"On the shores of Lyme Regis, where G.K. Chesterton takes his holidays, a strange sound haunts the night... Sister Seraphina and the other Sisters of Our Lady Star of the Sea have planned a seaside summer holiday for the students of Saint Wulfhilda's School. The mice of Saint Michael and Saint George Church welcome the group, and the beach awaits the excited students. But why is it so dangerous to go out at night? Sister Seraphina and her students will need all their wits to piece together the puzzling clues -- and save their holiday!