Gilligan's Planet

Let Sleeping Minnows Lie (1x3)

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The Skipper becomes despondent due to having been away from the sea and his boat for so long, so the others decide to build him a small boat, which serves the dual purpose of allowing the Professor to reach a small island which he thinks might be a source of mica, needed to repair their rocket. An attack by a sea monster leaves them stranded on the island, but not all is as it appears...