For each case there are several locations. Each chapter takes place in one location.
All levels for that chapter are contained on the screen in that location. For example the location might be in a house, or a factory, or a street. Levels are always ordered from left to right.
To start a level, just tap on it. Levels are unlocked in sequence, from 1 – 72.
To move to the next location at the end of a chapter, the player must pan to the right, then tap on the door. To move to the previous location, they must pan to the left and tap on the door. If it is the first chapter, then there is usually no door to go to the last location!
Sometimes, the panning is locked, and a level must be completed to move forward.