"All species in the world evolve...except one. Cancer Simplicimus Vulgaris, or the square crab, has suffered with the same evolutionary defect for millennia: it cannot change direction. Condemned to walk in one straight line forever, these crabs living along the Gironde estuary have largely resigned themselves to their fate. However, one seemingly ordinary summer, three crabs decide to take matters into their own claws and rebel against the straight...

Environmental mystery solvers Shelby and her best friend, Watts, who is never without his encyclopedia, must help Fred the hermit crab find all the shells that went missing from the beach.