I'm not sure if it has ever been mentioned but three mysteries by Chris Grabenstein are $.99 With $1.99 audiobook addon. They are:
1. Tilt-A-Whirl
https://www.amazon.com/dp/B000RGULAG/
2. Whack-a-Mole
https://www.amazon.com/dp/B000RGULAQ/
3. Mad Mouse
https://www.amazon.com/dp/B000RGULB0