Three men run a treasure hunt boat trip to a "haunted" castle on the small island that one of them (Dick Foran as Bill Martin) owns. One by one the party gets bumped off by a phantom, who uses secret passageways etc. Had this been made decades later add four meddling kids and a large dog and you would have a recipe for an episode of Scooby Doo.
Horror Island clocks in a at well paced hour. We get a mixed bunch of characters, Peggy Moran makes a very attractive leading lady and Fuzzy Knight (what a great name!) provides some laughs as Martin's sidekick. Far from being a Universal classic but I enjoyed it.