What secrets does the "desert island" hide?
One evening, the mummy family and little Mia embark, leave the old valley and set sail for a new home - Daddy's dream island with a lighthouse far out in the sea. It seems completely deserted at first, but it is not, strange things are happening there. Moomin's daddy, whose great wish is to understand the sea and his island well, decides to get to the bottom of all the mysteries...