First of all, if you're considering watching a Dean Martin-Jerry Lewis picture, you must be aware of the fact that it is mainly slapstick comedy. If you can't laugh at a drunk guy slapping Jerry Lewis in the face, then this movie isn't for you.
With that being said, this movie has an interesting story line. Lewis and Martin are friends and when Martin gets in trouble with Shorty, a mob-type guy, Lewis goes to defend him. This leads to an accidental shooting that Martin gets blamed for and when he goes to hide, he meets Mary, who inherited a haunted island from her father. Martin and Lewis end up going with Mary and figure out the mystery of Lost Island.
Although the plot jumps around a lot, watching Martin and Lewis is always enjoyable and there are many funny situations in this movie. If you're a fan of slapstick, this movie is for you.