The Secret of Seagull Island is a UK/Italian television series hacked down to a movie with added Giallo and some underwater diving scenes.
Barbara Carey (Prunella Ransome) has arrived in Rome to visit her blind concert pianist sister Marianne. Only she has gone missing. The third blind girl in recent months.
With the help of Martin Foster (Nicky Henson). From the British Consul who involves the police. Barbara investigates and she follows a lead to the private island of millionaire David Malcolm (Jeremy Brett) by pretending to be blind. David has a son who is deformed and Malcolm wants to help his son by bringing him blind women to befriend.
Meanwhile the police have been finding bodies of women with their eyes gouged at. Barbara gets attacked by seagulls on the island.
The movie does not make much sense because it was cut down. Even Brett's hamming cannot save this. It falls of a cliff by the end with a sub Psycho routine.