Survivors of a shipwreck are surprised to find rescue in the middle of the sea by none other than the renowned Capt. Nemo (Robert Ryan), who arrives in the Nautilus, his state-of-the-art submarine. As Nemo's guests soon discover, the eccentric genius has created an entire community at the bottom of the ocean. When the survivors find out that they can't leave Nemo's city, some of them rebel, causing a conflict that jeopardizes the lives of everyone in the undersea base.