Cam Jansen

#13 Cam Jansen and the Mystery at the Haunted House by David Adler, 1986, 1992.

Cam’s Aunt Katie and Uncle George take Cam and her friend Eric to an amusement park.  When they stop to buy food at the refreshment stand, Aunt Katie realizes that her wallet is missing.  She isn’t even sure exactly when it disappeared.  Cam thinks that someone stole her aunt’s wallet.  Who could have taken it?

Cam thinks at first that it might have been a couple of boys on roller skates who ran into her aunt earlier, but it wasn’t them.  Cam notices that another woman is complaining about a lost wallet and realizes that she had gone through the haunted house just before they did.  Someone in the haunted house is taking people’s wallets!

When they all go through the haunted house a second time, Cam figures out that a man dressed in black has been stealing people’s wallets.  When they went through the haunted house the first time, he jumped out at them, and they thought that he was just a part of the attraction meant to scare them.  She spots the man leaving the haunted house and tells the park’s security guards.  Everyone gets their wallets back, and the park’s owner gives Cam four free passes to the park for a month.

The book is currently available online through Internet Archive.