In a rock pool not too far from here, a tough but friendly Mussel spends his days working for the crabby and selfish Hermit Crab, H.C. Humans, not so affectionately known as “Big Ones” literally trash their habitat, littering the sea floor with debris. Worse yet, a tidal wave washes newcomers into the rock pool that these two shellfish share. Mussel befriends the newly homeless Urchin and Starfish, but H.C. orders the newcomers to leave on the next tide. The hungry but good-hearted Seagull arrives with a warning that two ships have collided, spilling tons of oil into the sea. Now, The Great Slick is coming their way, gleefully choking everything in his path. H.C. drives off Seagull, convincing himself that the warning is a ruse to allow the visitors to stay in what he considers to be HIS rock pool. New dangers arise, due to the actions of the unpredictable Giant Anemone and The Great Slick's mean advance scout Sludge. Can these appealing rockpool denizens pull together to survive all these threats, or will H.C.'s selfishness and close-mindedness doom them all?