At the water sprite and water nymph school, classes proceed as planned until the water nymphs leave for a dance competition and the water sprites accompany them to cheer them on. Only Vrbata, a notorious troublemaker, remains at the school as punishment. While exploring the cabinet, he carelessly awakens an octopus with living water. Upon the school trip's return, the octopus manages to capture the headmaster and begins to threaten the entire school. At the same time, the vagrant Mikolášek breaks into the school, so the water sprites, water nymphs, and teaching staff must not only fight the sea monster but also solve the problem of how to get rid of him. Unfortunately, nothing goes according to plan, and the octopus gradually captures everyone except the clumsiest water nymph, Křehulová. The situation begins to look hopeless. Fortunately, Mikolášek comes up with a plan and, together with Křehulová, tries to bring it to a successful conclusion...
Pavel Kříž
as Arnošt Tuňák
Jiří Ployhar
as Ráček
Jaroslava Kretschmerová
as Tanečková
Zuzana Volavá
as Marta Křehulová
Veronika Khek Kubařová
as Mrholová
Eliška Křenková
as Mechulová
Tereza Rumlová
as Rákosníková
Jiří Mádl
as Vrbata
Jiří Kout
as Lapil
Jakub Štěpán
as Polapil
Martin Písařík
as Mikolášek
