Singapore's coastline turns out to hold more biodiversity than its skyline suggests. This episode of David Attenborough's Wild City follows the creatures living along the city-state's shores and offshore islands, from a tiger tail seahorse hidden in seagrass to a cuttlefish flashing through color changes as camouflage and communication. The camera catches the yellow watchman goby and pistol shrimp sharing a burrow, the shrimp digging blind while the goby stands guard, a working example of two species trading labor for protection. Elsewhere a sand bubble crab rolls the beach into tiny pellets as it feeds, a dog-faced water snake hunts the mudflats, and a golden orb spider spins a web engineered to catch prey many times its size. The film also finds Neptune's Cup Sponge, a species once thought extinct and rediscovered in Singapore's waters. Attenborough's narration threads these encounters into a single argument: a densely built modern city and a working marine ecosystem are sitting right on top of each other.