From Bulbapedia, the community-driven Pokémon encyclopedia.
Come Out, Squirtle! (Japanese: でておいでよゼニガメくん Come Out Zenigame-kun) is written by Tomoaki Imakuni and illustrated by Naoyo Kimura. In English and Japanese, it is the second book in the Pokémon Tales series. It is 16 pages long.
A shy Squirtle is relaxing in a field, safely tucked into his shell. He refuses to leave his shell for any reason. A Charmander and a Poliwhirl try to convince it to come out of its shell, but Squirtle continually refuses. It rains, which Squirtle considers further proof that it should not leave its shell.
Finally, the rain stops. Charmander and Poliwhirl are staring in wonder at something, and although Squirtle is curious, it is still hesitant to leave its shell. Eventually, it does, and before it and the others is a beautiful rainbow which appeared after the rainstorm. Squirtle decides it is glad that it left its shell after all.
When Squirtle's friends convince the tinyturtle to overcome its fears and come out of its shell, Squirtle is just in time for a beautiful surprise!
No humans appear in this book.