The subs help a pod of Baltic Sea grey seals find a new iceberg home… but then they can’t get rid of the grateful seals, who follow them around disrupting their work!

While on a deep sea adventure Olly discovers many strange phenomena, including a disappearing shipwreck and some interesting deep sea fish.

Olly and Beth explore an underground river and discover the secrets of an ancient sinkhole.

In trying to buddy up to Brandt, Bobsie Otter fibs about having a real treasure map and he almost loses his newfound friend – for good!

Skid, tired of always doing the messy work, plays hooky from his job. Knowing Diver Doug will be unhappy with him, he pretends he has been captured by a terrible Sea Creature! When Olly and Beth discover his ruse, they turn the tables on Skid to teach him a lesson.

Beth and Olly visit a special underwater cave with Dr. Daniels to photograph the prehistoric artwork inside. When Dr. Daniels runs into trouble with her oxygen tank, Beth uses the cave paintings to find her an alternative way out.

Olly wants to prove to Dr. Daniel what a great research sub he is by finding a special artifact for her in the Mediterranean Sea. Only Olly hasn’t yet learned the proper way to retrieve artifacts – and he almost ruins it!

The subs join Dr. Kate at the opening of the Shanghai Marine Museum. Skid joins them, but soon feels left out as Walter and the subs reminisce together.

With Sub D coming, Beth works hard to clean up and breaks her nose light in the process. She’s forced to wear a huge replacement nose instead.

Bobsie goes in search of a mermaid and ends up helping save a manatee from the perils of a speedboat.