Does David still carry the guilt of not sticking with his vulnerable friend? How much more would he be carrying if he knew the voices in her head were real? How much more if he knew her 'imaginary' demon had carried away her lifeless body that night? Look out for your friends, my friends. 
Elmwych Comic P.41
Panel 1: David and Emily are about to enter a nightclub called Fuchsia. He wears a Frankenstein's monster costume and she is dressed as an Egyptian mummy. It's night and they are surrounded by others in fancy dress.
David (caption): Her medication seemed to be working for a while...
Emily: That creepy voice again! Can't you hear it?
David: No!
Panel 2: David and Emily are inside the club. A white haired woman is sitting in the foreground, clutching a hat box on her knee.
Emily: Over there! The girl with the white hair! The voice is coming from that box!
David: Did you take your pills?
Panel 3: David and Emily talking in the foreground. The white haired woman is visible behind them.
Emily: Thanks for that vote of Confidence David. I'm going outside for some fresh air.
David: Don't be long!
David (caption): Why didn't I follow her?
Panel 4: As Emily walks away, a close up of the white haired woman shows a fractured voice emerging from her hat box.
Fractured voice: It is true - she hears us! You know what to do.
Panel 5: Outside the club in a deserted street we see Emily at a distance, holding her head in her hands. The partial figure of the white haired woman is visible in the foreground, holding a large kitchen knife.
Emily (thinks): Get a grip Emily, it's all in your mind!
Panel 6: A large red demon like creature carries the limp, blood soaked body of Emily over it's shoulder and walks into the distance. In the foreground the discarded knife lies on the road and a large pool of blood stretches toward us.
David (caption 1): And that's the last time I saw her. I should've been there...
David (caption 2): ...when she needed a shoulder to lean on.