Pill hunters:Between The shadows

I'm gonna say NYC or any other huge city (your choice) Teen girl or boy (your choice) visiting some of the famous sites. They wander off into a less densely populated area (as all storybook teens in this situation do) and when they come back, everyone is gone. Not just thier family, everyone. Suddenly the get a pounding headache. They close thier eyes as tight as they can, that multi colored light blooming behind thier eyes. When they open thier eye they see flashes of black shadows. Shadows in human shape. The shadows begin chasing them and they can hear shrill screams emminating from no where. They barricade themselves in a bathroom. Of course it just happens to be the bathroom for the opposite gender of your main character where they meet their romantic intrest the only other person who dosen't seen to be a shadow. Now, these shadows never stop screaming, the shrill whine is always in the back of the two character's minds. (Perhaps for a plot twist towards the end the screaming could stop and that would mean something significant.) The shadows aren't there to kill or at least they don't seem to be. When a shadow touches the characters they are encased in darkness, unable to see, and the only thing that seems to destroy them is fire which is kind of hard to find in a metropolis.
After being inside a shadow, the main characters are left with an appropriate sense of terror. Slowly, as you can imagine all the screaming and the burning shadows (when they're set on fire theyscream even louder.) Begins to get to them, pounding headaches snapping at each other for no good reason etc. They're also terrified of the coming night because the lights in the area out side the bathroom (lobby for example) automatically go off after closing time. Without lights they won't be able to see the shadows. Horror and Romance