@summerjo Are you 100% positive you left it in Emma's house?
If not, try placing it in the shower/mother's bedroom again.
If that doesn't work, and you still have the previous version, try loading that up instead and see if you can get the camera back that way.
If that doesn't work, or previous version isn't an option, try regedit (HKEY_CURRENT_USER/Software/KsT games/The Twist) and go to the entry for the spycam (_spycam_h2955864655, the only spycam entry) and change it to a 0*.
Load up the autosave, and buy the cam again.
*if the registry entry has the spycam with a 0 already, change it to a 1 and load the autosave