Finland, June. White nights and summer vacations. However, for eleven-year-old Hilla, nine-year-old Kasper, and six-year-and-four-month-old Maya, these vacations begin in the most paradoxical way. When their mother wins a two-week trip to Lapland, she receives not only the tickets but also a surprise gift in the mail: a nanny to look after the children. However, this is not an ordinary nanny, but a huge fluffy creature that smells of mold and does not speak! "Host family: Hellman. Species sent: A trained almost-human, commonly known as a 'monster,' specializing in child care and household chores." When the three siblings discover that other neighborhood children also have a monster-nanny at home, the mystery deepens. Where did the monsters come from? Who is behind all this?