Humongous (1982)

Labour Day, 1946, a party outside a mansion on a night enshrouded island, teenager Ida Parsons leans towards a cage where her guard dogs stare, their heads cocked and doe-eyed at her before she is is confronted by Tom Rice clearly the worse for drink - whose advances she spurns; escaping off into the nearby woods. He follows her, tracking her down, and then pushing her to the ground, despite her pleas for him to stop, set upon and raped before the eyes of her faithful hounds, she'd been cooing over moments previously. They break free to come to the aid of their violated mistress and savagely maul the rapist before she brings a rock down onto his head. But she has been left with a child. Cut to the early eighties and three siblings; brothers Nick (seriously headstrong) & Eric Simmons and their younger sister Carla/Sarah together with their partners, Sandy/Teddy Ralston, teen fashion model wannabe Donna Blake and stranded sailor Bert Defoe find themselves in a fogbound night only to run aground on the rocks of the mysterious 'Dog Island' right before their boat goes up in flames. As they gather on the shoreline one of them goes missing, another is critically injured and four go searching for shelter and decide to venture into the still standing house to summon help from it's occupants...if any. Luckily there is someone still dwelling there and unfortunately there's a reason why he was kept here since there's something else out on the island growling in the dark and it ain't no dog!