When his mother brings home a guinea pig instead of the dog he has always wanted, fifth-grader Rufus is not happy--until the rodent starts acting exactly like a dog.

While his human Elliot adjusts to his new home and stepfamily, Gizmo, an evil genius guinea pig, searches for a new evil lair where he can plot to take over the world, but Gizmo is constantly thwarted by Elliot's little stepsister Jasmine (who likes to play dress-up), Abuela (who may or may not like to eat cavies), and Wedgie (a Corgi superhero and Gizmo's nemesis).

When his friend Soldier hurts his head, Little Whistle tried to find something to make him feel better so he will be able to read the other toys their bedtime story.

A boy who thinks his sister's new guinea pig is a very boring pet imagines what it would be like to have a dog, a bear, or even a dragon instead.

Sasspants, the reluctant guinea pig private investigator, is drawn into another mystery by Hamisher the hamster who believes there is a ghost in the pet shop.

Guinea pig Sasspants knows something is wrong with ninth-grader Viola, the new pet shop assistant, so when Mr. Venezi goes missing Sasspants and Hamisher put their private investigation skills to the test.

Mr. Gilbert brings in a guinea pig as a class pet, but it looks so lonely he brings another, and before long the class is getting an unexpected lesson in addition--and a very full cage.

When Nibbles the guinea pig and his friend Posie find caterpillars munching on their prize-winning dandelion plants, they decide to make the caterpillars their pets.

When guinea pig Sasspants leaves Mr. Venezi's pet shop to live with Detective Nichols, and hamster-detective Hamisher retires, the case of the missing bookstore cat must be solved without their help.

As Christmas nears, Amy and her friends in the Critter Club try to find a home for two adorable guinea pigs.