Deep in the peaceful ocean where there is never any crime, three valuable treasures go missing. With no one to help the victims Carrie Crab, Susie Seahorse and Johnny Jellyfish, a determined but naive young Octopus decides to become the first ever underwater detective. The Octopus Detective armed with his special waterproof detective notebook, a starfish for a badge and no idea how to investigate crime, sets off to solve the case.