In "Tom Swift and His Undersea Search," Tom and his friends set out on an adventure to search for a treasure said to be located on the floor of the Atlantic Ocean. They use a state-of-the-art underwater diving vessel to explore the ocean depths and face many challenges, including dangerous sea creatures and treacherous underwater terrain. Through their bravery and determination, Tom and his friends are able to locate the treasure and make a great discovery that will change their lives forever.