The Lemon Beach House, run by the Aizawa sisters, is booming with customers in the middle of the summer. This peace will be short-lived. A girl calling herself "Ika Musume" (Squid Girl) emerges from the sea, stating her goal of taking over the world as a revenge on humanity for polluting the oceans. This army of one has a long way to go, though. When she breaks a large hole in the beach house, the sisters force Ika to work for them until she can pay for the repairs. Thus begins a cute comedy about the friends at the Lemon Beach House and world domination... supposedly.