Set in and around the remote tidal island of Amen, Unhappy Birthday is the fictional story of three outsiders' battles against the twisted morals of an antiquated community. Inspired by British cult classics such as The Wicker Man and Hammer House of Horror, the film explores the fear of isolation and nature versus nature. A special birthday party becomes a living nightmare for City-dwelling couple Sadie and Rick and their friend Johnny. They visit Corinne, an enigmatic local on the island of Amen, which is accessible only by invite and seemingly impossible to get off. A mysterious family connection with Corinne brings horrific consequences as they find themselves trapped by the tide and at the mercy of the island's wild nature.

A city-dwelling couple and their friend are invited to the remote tidal island of Amen for a surprise birthday party that turns into a living nightmare.