Someone called 911 and it is a serious case. Probably, one that would involve a lot of lives, if the authorities won't do anything to stop it. Fortunately, the authorities will not let that happened as they are quick in going to the scene of the crime. The bomb disposal unit recover the bomb and will try to diffuse it for sure.
This game takes more than just diffusing the bomb as you need to park your car too. When you get the bomb, you will get a few seconds to diffuse it. Once that, you accomplish that, you would need to park your car before you can advance to the next level.