Sasspants, a guinea pig, reluctantly agrees to act as a private investigator when Hamisher the hamster begs for her help in discovering who is stealing sandwiches from the pet shop's befuddled owner.

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.

"Sasspants, Hamisher, and company have never been so raucous at the Mr. Venezi's Pets And Stuff pet supplies shop. This time, there's scuba-diving in the fish tank with the Steves, what appears to be a dragon hiding behind the counter, and Mr. Venezi's insistence that the store has been robbed of exactly sixty-four dollars and forty-two cents"--