Octie Octopus and Milly Mermaid are sitting in Octie's den when Octie admits to feeling sad. He longs to see and learn about other ocean animals, but he can't swim very far. He can't travel the world like his friend Milly, although he wishes he could. How will Milly make Octie happy again? She's got an idea!

Milly takes a seashell from her hair. Little does Octie know that the seashell is magical. With her seashell, Milly draws a picture of a seahorse. A moment later, the seahorse drawing springs to life! Octie gets to meet Samuel Seahorse, and so the educational adventure begins.

More new friends arrive with Milly's help, and Octie learns all about other ocean creatures and their lives. Not only does he learn about them, but he also makes friends with them. Octie's dream of exploring the ocean comes true, and he never even leaves the house. Come along with Octie and Milly and meet all the amazing creatures of the sea.