Teenager Jana Vodiczkova (Libuše Šafránková), an ordinary high school student, is different from others around her because she is a “water spirit”. She lives with her family in an old house on the banks of the Vltava River, and during the holidays she enjoys spending time at the pool. It is there that she rescues the life of the drowning doctor Mraczkowi (Jaromir Hanzlik), not knowing that the members of her family, headed by the despotic Wasserman, are responsible for the attempt at sending the doctor six feet under. The reason for the attack on doctor Mraczek is that he, being an employee of the housing office, received the task of transferring the Vodiczki family from a damp house to a block of flats with central heating.