When Dawn gets a last-minute weekend sitting job at the Mancusi's house, she isn't exactly thrilled because she's not an animal lover like Kristy & Mary Anne, but she ends enjoying herself at the Mancusis. Then on Sunday, when Dawn is feeding & taking care of the other animals, she notices that the Mancusi's Great Dane dog, Cheryl needs to go outside, so Dawn takes her outside & clips her lease to the secure lead that the Mancusis keep in the front yard.
After finishing up the indoor animal chores, Dawn gets the other two dogs ready for their walk and when she goes outside to the yard to get Cheryl, she is nowhere to be found. The chain isn't broken, so Dawn thinks that somebody let her off the lead as a prank. The other club members and sitting charges help look for Cheryl, but they don't have any luck finding her. Dawn feels horrible about what happened even though the Mancusis are nice about the whole thing when they get home and hear the news.
Not long after Cheryl goes missing, the BSC is getting ready for a club meeting, but Kristy isn't there on time. When she finally shows up, Kristy says that her dog, Shannon went missing in the exact same way that Cheryl did: David Michael clipped her to her lead in the yard, went inside for a toy, and when he came back, she was gone. The girls make lost dog posters for both Shannon and Cheryl, hoping that somebody knows where they are.
Later that evening, Dawn reads the newspaper and reads an article about a rash of missing dog cases in Stoneybrook & other nearby towns. The police think that a professional dog theft ring might be responsible. Dawn remembers the car that followed her when she was walking the Mancusi's dogs. The girls look for the license plate number, but their first day of searching isn't successful, but on the second day, Kristy & Dawn find it. When the girls take to the police station, the officer on duty doesn't take Dawn seriously, but Dawn forces the license plate number on him anyway. After not hearing from the police, Dawn figures that somebody in her family missed the call.
When Dawn, Mary Anne, and Kristy go back to the police station the next day to ask about the license plate number in person, they discover that the car belongs to Karl Tate, one of the richest businessmen in Stoneybrook. The girls don't believe that he has anything to do with the dog thefts, but as Dawn & Mary Anne stop at a new pet store to get something for tigger, they notice Karl Tate in the back office of the store arguing with the store owners which makes Dawn believe that he is responsible for the dog thefts, but she doesn't know how to prove it.
The girls decide to put Karl under surveillance. The first day doesn't get them any results, but the second day does; Kristy, Dawn, & Mary Anne go back to the pet store because Dawn wants to get a more better idea of how they operate. Dawn is able to get a good look at what the store has and she asks the owner what they don't have in stock (such as a Saint Bernard). The salesbreeder tells Dawn that they could get her a Saint Bernard if she could pay. Meanwhile, Kristy and Bart have chosen some players from their respective baseball teams to combine an all-star team called the Krashers. The Krashers are playing a baseball team from New Hope. When Dawn decides to take a break from thinking about the missing dogs & enjoy the game, she notices a woman jogging by with Cheryl. Dawn sends Mary Anne to stall her if she can while she calls the police. When the police show up, they question the woman. Her timeline for getting Cheryl matches up with when she disappeared from the Mancusis' backyard and the woman is more than happy to give her back.
After the game, Mr. Pike takes Mary Anne & Dawn to the police station to see how the case is. It is revealed that Karl Tate was responsible for the dog thefts because he had been losing a lot of money in real estate, so he came up with a bunch of money-making schemes including the pet store. They've tracked down most of the stolen dogs (including Shannon) and are reunited with their owners.
Dawn feels terrible when he pet-sitting charge, Cheryl, disappears. She doesn't understand how the huge Great Dane just...vanished.
Then Kristy's puppy Shannon turns up lost, too, and Dawn knows something suspicious is going on. She doesn't think the dogs have run away. Dawn believes that someone's taken them. And she's determined to find those missing dogs. Because what could be more awful than having your favorite pet...stolen?!