Dr Su Hong is a famous marine researcher and underwater archaeologist. He has four imitations of ancient medals hidden in the deep sea by pirates of the Caribbean. The four medals represent wisdom, courage, friendship and justice. On this day, Dr. Su Hong called Ali and Beibei and told them that if they could complete the task, they would get a medal. If four medals can be collected, the little ones will be invited to Quanzhou to attend the opening ceremony of the Ocean Museum, and they will receive the mysterious award from the doctor, which will make the little submarines excited and eager to try.

Ali and Beibei, together with frog, pet monkey Tao Tao, stone scooter and other small partners, worked together in unity and did not fear difficulties, and successively completed the tasks of searching for the Egyptian Queen in the Mediterranean Sea, searching for Perth wreckage in the Arctic Ocean, searching for ancient slates in the Arabian Sea, and integrating and protecting sunken cultural relics. They have won four medals from doctors and returned to Quanzhou. After a soul-stirring search, they found the anchor of Zheng He's shipwreck and gave this precious cultural relic as a gift to the Quanzhou Ocean Museum, which is about to open.

The small submarines completed all the tasks given to them by Dr. Su Hong, and Dr. Su Hong kept her promise. She arranged to set off fireworks in the image of a small submarine as a surprise reward at the opening ceremony of Quanzhou Ocean Museum.

Through the experience of ocean exploration, small submarines not only become more mature, brave, United and cooperative, but also learn a long history of marine civilization and a lot of useful knowledge about the protection of marine cultural relics, and become real submarine heroes.