Mystère sous la glace (Enigma Under the Frozen Lake)

This is the 5th book in the Series "Les aventures d'Olivier et Magalie". Olivier and Magalie are brother and sister and often spend holidays with their grandparents at their lake house. They, with new friends they meet at the lake, are always discovering mysterious objects or situations...and eventually resolve the enigmas after much adventurous action and suspense. Stories that will captivate both boys and girls.