Stacey and Charlotte Johanssen have a big day planned; they’re going shopping and have lunch in Downtown Stoneybrook & they’re both excited. Things go well until Stacey tries to buy some earrings at the Merry Go-Round. The clerk immediately recognizes the $10 bill that Stacey gives her as counterfeit, much to Stacey’s surprise. Betty, the clerk calls the police; she doesn’t suspect Stacey, but there has been some counterfeit activity in Stoneybrook & the police need to be aware of what happened.
Charlotte is worried that Stacey is going to jail, but the cops just want to ask Stacey, Betty, and the clerk at Bellair’s (where Stacey got the $10 bill from). Stacey’s mom looks after Charlotte while Stacey is being questioned. The other girls in the BSC decide that they need to do some research on counterfeiting; they go to the library and even pay a visit to Betty at the Merry-Go-Round to pick up a flier that had been given to all local shops about how to spot counterfeit bills.
The girls also decide to stake out various public copy machines around Stoneybrook. They notice Stacey’s English teacher, Mr. Fiske looking at new copy machines and think he could be the suspect, but nobody thinks so. Kristy thinks it might be a new boy in school named Terry Hoyt & his family, who are responsible for all the fake money. They showed up right around the time that the counterfeiting started, they move around a lot, and there’s a closet in their house that Terry’s younger brother, Georgie wouldn’t let Kristy open when she was babysitting. Kristy also found a school ID card belonging to Terry’s twin sister, Tasha with a different name.
Stacey doesn’t want to believe that the Hoyts are responsible because Stacey likes Terry and she doesn’t see him as being capable of doing something like that. The BSC follow Mr. Fiske one day after school, but it’s unsuccessful. After Stacey gets home, she gets a phone call from Terry & she ends up telling him everything that they’ve been up to. Terry seems to know a lot about counterfeiting, but he doesn’t come right out and confess that his family’s responsible.
Later on, Stacey and Charlotte go on another shopping trip downtown. As they’re about to head over to the Rosebud Cafe for lunch, a man runs toward them. As he’s running, the man drops a bag full of fake money, but doesn’t get it. Charlotte suggests calling the police, but Stacey wants to solve the case herself. She gets Claudia to come down to take a picture of the man when he comes back from the money & she calls Terry herself. After waiting a while, the man comes back & they get their pictures.
Stacey and Terry take a roll of film to a one-hour photo place & Terry says that he can give the pictures to his father when they get them & he’ll take care of everything. At first Stacey worries because she thinks Terry & his family are responsible for the counterfeits, but it turns out that Terry’s father is in the Secret Service & is the main guy assigned to work on the counterfeiting case. The reason the Hoyts move around so much is because once a case is solved, they move on to another place. Terry’s real name is David Hawthorne & Stacey is sworn to secrecy that no one is supposed to know what his dad does for a living. In the end, the counterfeiters are caught & the Hoyts have to move on once the case is over.
Who would have believed it? Counterfeit money is showing up in Stoneybrook – and someone gave Stacey a fake ten dollar bill.
Of course Stacey doesn't have anything to do with the counterfeit money. But the Baby-sitters are worried. They think one of their clients might be involved. And what if people don't believe Stacey is...innocent?
The Baby-sitters have to discover where this mysterious money is coming from. Because their reputation is at stake!