New Year"s loss. Fluffy detective

On New Year"s Eve, when all letters were read and gift bags were prepared, the misfortune happened: Santa Claus forgot an important letter from the boy Nikolka on the table, and it disappeared. Who took the letter? The mischievous hollow Ryzhik? Noisy knobs? Or a shy baby Ushastik, who wants to become an assistant to the grandfather? But whoever is to blame, you need to urgently find the loss, otherwise the grandmother of Nikolka will not receive a gift for the holiday.
Red-haired and ears will become the most real detectives: they will try to trace the path of lost letter and take part in the important scientific Isle-Do-Vaniy, having made many discoveries.
The book is addressed to children from 5 years old