Protect the energy diamonds!
To move, press anywhere on the screen, and the messengers will accelerate towards that position, moving faster the farther away it is. the red dragons will swarm the energy diamonds in the middle of the screen, and you have to run into them and push them away so that they won't drain all the energy from it. You have been provided with a rainbow laser cannon that charges while enemies are off the screen. Be aggressive, push them off, and when your yellow charge meter starts flashing, you can tap a second finger on the screen to aim the weapon, which utterly disintegrates all red dragons in its path. The trips between green and orange cities take 103 seconds, and so does each level. You lose if the dragons eat the diamond.
The game gets harder as time goes on, as dragons speed up, you will sometimes have to protect more diamonds, and they will start to send more messengers to help you out.
No matter what, though, life in the cities goes on.