After returning from the planet Almoa, Sigrid, who serves in the Space Department, begins to become covered in scales every time water hits her skin. To recover from her illness, she goes to the Septentrion galaxy, whose fertile climate promises healing. But, finding herself on a distant planet, the girl finds herself in a new trouble: a huge dragon lives in the ocean, which eats the continents along with their inhabitants. If Sigrid sits idly by, he will become easy prey for the terrible monster. She decides to take a brave step - not just to save her own life, but also to prevent the dragon from destroying all living things. Having cunningly penetrated the belly of the monster, Sigrid does not even suspect that she has fallen into a skillfully placed trap. When she manages to reveal the secret so carefully guarded by the Great Serpent, she understands that there is practically no chance of salvation...